taler-docs

api-merchant.rst (215461B)

---

 ..
   This file is part of GNU TALER.
   Copyright (C) 2014-2025 Taler Systems SA
 
   TALER is free software; you can redistribute it and/or modify it under the
   terms of the GNU Affero General Public License as published by the Free Software
   Foundation; either version 2.1, or (at your option) any later version.
 
   TALER is distributed in the hope that it will be useful, but WITHOUT ANY
   WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
   A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more details.
 
   You should have received a copy of the GNU Affero General Public License along with
   TALER; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
 
   @author Marcello Stanisci
   @author Florian Dold
   @author Christian Grothoff
   @author Priscilla Huang
   @author Martin Schanzenbach
 
 .. _merchant-api:
 
 ============================
 Merchant Backend RESTful API
 ============================
 
 ---------------
 Version History
 ---------------
 
 The current protocol version is ``v20``.
 
 Android PoS app is currently targeting ``v20``.
 
 **Version history:**
 
 * ``v21`` (in development): Adds self-provisioning and two factor authentication.
 
 -----------------------
 Base URLs and Instances
 -----------------------
 
 A single merchant backend installation can host multiple merchant instances.
 This is useful when multiple businesses want to share the same payment
 infrastructure.
 
 Merchant backends have one special ``admin`` instance.  This ``admin``
 instance is used when no explicit instance is specified.  Note that using
 ``/instances/admin/$ANYTHING`` is deprecated and will result in a permanent
 redirect (HTTP status 308) to ``$ANYTHING``. a Despite its name, this instance
 must be created after the installation.
 
 Each instance (admin and others) has a base URL.  The resources under
 this base URL are divided into to categories:
 
 * Public endpoints that are exposed to the Internet
 * Private endpoints (under ``/private/*``) that are only supposed to be exposed
   to the merchant internally, and must not be exposed on the
   Internet.
 * Management endpoints (under ``/management/*``) are also private and dedicated
   to CRUD operation over instances and reset authentication settings over all
   instances. Only accessible with the admin instance authentication token.
 
 Examples:
 
 .. code-block:: none
 
    Base URL of the merchant (admin instance) at merchant-backend.example.com:
    https://merchant-backend.example.com/
 
    A private endpoint (admin instance):
    https://merchant-backend.example.com/private/orders
 
    A public endpoint (admin instance and order id "ABCD"):
    https://merchant-backend.example.com/orders/ABCD
 
    A private endpoint ("myinst" instance):
    https://merchant-backend.example.com/instances/myinst/private/orders
 
    A public endpoint ("myinst" instance and order id "ABCD"):
    https://merchant-backend.example.com/instances/myinst/orders/ABCD
 
    A private endpoint (explicit "admin" instance):
    https://merchant-backend.example.com/private/orders
 
    A public endpoint (explicit "admin" instance):
    https://merchant-backend.example.com/orders
 
    Endpoints to manage other instances (ONLY for implicit "admin" instance):
    https://merchant-backend.example.com/management/instances
    https://merchant-backend.example.com/management/instances/$ID
 
    Endpoints to manage own instance:
    https://merchant-backend.example.com/private
    https://merchant-backend.example.com/private/auth
    https://merchant-backend.example.com/instances/$ID/private
    https://merchant-backend.example.com/instances/$ID/forgot-password
    https://merchant-backend.example.com/instances/$ID/private/auth
 
    Unavailabe endpoints (will return 404):
    https://merchant-backend.example.com/instances/myinst/private/instances
 
 -----------------
 Generic Responses
 -----------------
 
 The following (error) responses are applicable to all endpoints
 unless specified otherwise.
 
 .. http:any:: *
 
   :http:statuscode:`403 Forbidden`:
     * ``TALER_EC_GENERIC_FORBIDDEN``: Missing permissions.
     * ``TALER_EC_MERCHANT_ACCOUNT_TWOFA_UNCONFIRMED``: The account
       needs to confirm authentication factors before it can proceed
       with the request.
 
 --------------
 Authentication
 --------------
 
 Each merchant instance has separate authentication settings for the private API resources
 of that instance.
 
 Currently, the ``/private/auth/`` API supports two main authentication methods in the ``InstanceAuthConfigurationMessage``:
 
 * ``external``: (@deprecated since **v20**) With this method, no checks are done by the merchant backend.
   Instead, a reverse proxy / API gateway must do all authentication/authorization checks.
 * ``token`` (**@since v19**): With this method, the client must provide an authorization header
   that contains a bearer token  when accessing a protected endpoint in the form
   ``Authorization: Bearer secret-token:$TOKEN``.
   ``$TOKEN`` is an authentication token retrieved from the ``/private/token`` endpoint using basic authorization.
   The respective username is the instance ``$ID``, and the password the instance password (``$INSTANCE_PASSWORD``).
   A login token is commonly only valid for a limited period of time and scoped to specific permissions.
   If the ``$INSTANCE_PASSWORD`` is lost, the administrator can set a password
   using the ``taler-merchant-passwd`` command-line tool.
 * ``token`` (@deprecated since **v19**): With this method, the client must provide an authentication token in
   the format ``secret-token: $INSTANCE_PASSWORD``.
   The behaviour is then equivalent to the ``token`` method above.
   Any API may be accessed using the bearer authentication ``secret-token: $INSTANCE_PASSWORD``.
   Notice that this behaviour is deprecated and will be phased out in favor of login tokens.
 
 For testing, the service may be started with the configuration option ``DISABLED_AUTHENTICATION = YES``
 in section ``[merchant]`` (@since **v20**).
 
 Scopes
 ^^^^^^
 
 Access tokens can be requested with a (limiting) scope. Available scopes and their associated permissions are:
 
 * ``readonly``: ``*-read`` -- Access to APIs using ``GET`` requests is always allowed.
 * ``write`` (*deprecated*): See ``all``.
 * ``all``: ``*`` -- General access to all APIs and endpoints and always refreshable. (@since **v19**)
 * ``spa``: ``*`` -- General access to all APIs and endpoints. (@since **v20**)
 * ``order-simple``: ``orders-read``, ``orders-write`` -- Allows the creation of orders and checking of payment status. (@since **v19**)
 * ``order-pos``: ``orders-read``, ``orders-write``, ``inventory-lock`` -- Same as ``order-simple`` and allows inventory locking. (@since **v19**)
 * ``order-mgmt``: ``orders-read``, ``orders-write``, ``orders-refund`` -- Same as ``order-simple`` and also allows refunding. (@since **v19**)
 * ``order-full``: ``orders-read``, ``orders-write``, ``inventory-lock``, ``orders-refund`` -- Same ``order-pos`` and ``order-mgmt`` combined. (@since **v19**)
 
 Since **v19** the scope may be suffixed with ``:refreshable``, e.g. ``order-pos:refreshable``.
 This allows the token to be refreshed at the token endpoint.
 This behaviour replaces the deprecated ``refreshable`` field in the `LoginTokenRequest`.
 
 -----------------
 Configuration API
 -----------------
 
 The configuration API exposes basic information about a merchant backend,
 such as the implemented version of the protocol and the currency used.
 
 .. http:get:: /config
 
   Return the protocol version and currency supported by this merchant backend.
   This specification corresponds to ``current`` protocol being version **v24**.
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The body is a `MerchantVersionResponse`.
 
   **Details:**
 
   .. ts:def:: MerchantVersionResponse
 
     interface MerchantVersionResponse {
       // libtool-style representation of the Merchant protocol version, see
       // https://www.gnu.org/software/libtool/manual/html_node/Versioning.html#Versioning
       // The format is "current:revision:age".
       version: string;
 
       // Name of the protocol.
       name: "taler-merchant";
 
       // URN of the implementation (needed to interpret 'revision' in version).
       // @since **v8**, may become mandatory in the future.
       implementation?: string;
 
       // Default (!) currency supported by this backend.
       // This is the currency that the backend should
       // suggest by default to the user when entering
       // amounts. See ``currencies`` for a list of
       // supported currencies and how to render them.
       currency: string;
 
       // Which Persona should be used by default by new clients in the SPA.
       // Can be changed locally per browers under "Personalization".
       // Possible values include "expert", "offline-vending-machine",
       // "point-of-sale", "digital-publishing", "e-commerce" and "developer".
       // @since **v23**.
       default_persona: string;
 
       // How services should render currencies supported
       // by this backend.  Maps
       // currency codes (e.g. "EUR" or "KUDOS") to
       // the respective currency specification.
       // All currencies in this map are supported by
       // the backend.  Note that the actual currency
       // specifications are a *hint* for applications
       // that would like *advice* on how to render amounts.
       // Applications *may* ignore the currency specification
       // if they know how to render currencies that they are
       // used with.
       currencies: { currency : CurrencySpecification};
 
       // Array of exchanges trusted by the merchant.
       // @since **v6**.
       exchanges: ExchangeConfigInfo[];
 
       // Set when the merchant supports
       // self-provisioning instances.
       // Since protocol **v21**
       have_self_provisioning: boolean;
 
       // True if this merchant backend supports the Donau
       // extension and can thus issue donation receipts.
       // Should primarily be used to control the SPA's CRUD
       // functionality for Donau.
       // @since **v21**
       have_donau: boolean;
 
       // Tan channels that are required
       // to be confirmed for an instance to
       // be useable.
       // @since **v21**
       mandatory_tan_channels?: TanChannel[];
 
       // Space-separated list of enabled payment target types.
       // Useful if the SPA should not show allow adding other
       // types of bank accounts. "*" is used to represent no
       // restriction.
       // @since **v22**
       payment_target_types: string;
 
       // Regular expression representing further restrictions
       // on allowed payment targets.  Any "payto://"-URI supplied
       // for a bank account must match the given regular expression.
       // For example, "payto://iban/CH.*" would restrict the system
       // to only Swiss bank accounts.
       // Optional, no restrictions are imposed if the field is
       // absent.
       // @since **v22**
       // CAUTION: Likely to be removed/deprecated,
       // as we'll want an array of restrictions with the
       // same format as the exchange uses, as this allows
       // proper i18n and spec/code reuse.
       payment_target_regex? string;
 
       // Default payment delay for new instances.
       // This is the default to use for new instances, see the instance value for
       // the instance-specific default.
       // A value of "forever" is not allowed.
       // @since **v22**
       default_pay_delay: RelativeTime;
 
       // If the frontend does NOT specify a refund deadline, how long should
       // refunds be allowed by default?
       // This is the default to use for new instances, see the instance value for
       // the instance-specific default.
       // A value of "forever" is not allowed.
       // @since **v22**
       default_refund_delay: RelativeTime;
 
       // Default wire transfer delay for new instances.
       // This is the default to use for new instances, see the instance value for
       // the instance-specific default.
       // A value of "forever" is not allowed.
       // @since **v22**
       default_wire_transfer_delay: RelativeTime;
 
       // Default interval to which wire deadlines computed by
       // adding the wire_transfer_delay on top of the refund
       // deadline should be rounded up to.
       // @since **v23**
       default_wire_transfer_rounding_interval: RoundingInterval;
     }
 
   .. ts:def:: TanChannel
 
     enum TanChannel {
       SMS = "sms",
       EMAIL = "email"
     }
 
   .. ts:def:: RoundingInterval
 
    enum RoundingInterval {
       NONE = "NONE",
       SECOND = "SECOND",
       MINUTE = "MINUTE",
       HOUR = "HOUR",
       DAY = "DAY",
       WEEK = "WEEK",
       MONTH = "MONTH",
       QUARTER = "QUARTER",
       YEAR = "YEAR"
     }
 
   .. ts:def:: ExchangeConfigInfo
 
     interface ExchangeConfigInfo {
 
       // Base URL of the exchange REST API.
       base_url: string;
 
       // Currency for which the merchant is configured
       // to trust the exchange.
       // May not be the one the exchange actually uses,
       // but is the only one we would trust this exchange for.
       currency: string;
 
       // Offline master public key of the exchange. The
       // ``/keys`` data must be signed with this public
       // key for us to trust it.
       master_pub: EddsaPublicKey;
     }
 
 .. include:: tos.rst
 
 ---------------
 Two Factor Auth
 ---------------
 
 202 Challenge Responses
 ^^^^^^^^^^^^^^^^^^^^^^^
 
 Various APIs generate ``202 Accepted`` HTTP status codes when multi-factor
 authentication (MFA) is required.  In this case, the response will be a
 `ChallengeResponse`.  In these cases, the client must first request and solve
 one or more challenges before repeating the request. When repeating the
 request, they must include a list of comma-separated challenge IDs of the
 solved challenges in an ``Taler-Challenge-Ids`` HTTP header. The body must
 remain absolutely unchanged.
 
   .. note::
 
     If all allowed attempts to solve the MFA challenge(s) fail, the endpoint
     may start to return ``403 Forbidden`` until the issued challenges expire,
     preventing the request from being completed for a while.  In this case,
     repeating the request with a different body may still be allowed!
 
   .. ts:def:: ChallengeResponse
 
     // @since v21
     interface ChallengeResponse {
       // List of challenge IDs that must be solved before the
       // client may proceed.
       challenges: Challenge[];
 
       // True if **all** challenges must be solved (AND), false if
       // it is sufficient to solve one of them (OR).
       combi_and: boolean;
 
     }
 
   .. ts:def:: Challenge
 
     interface Challenge {
       // Unique identifier of the challenge to solve to run this protected
       // operation.
       challenge_id: string;
 
       // Channel of the last successful transmission of the TAN challenge.
       tan_channel: TanChannel;
 
       // Info of the last successful transmission of the TAN challenge.
       // Hint to show to the user as to where the challenge was
       // sent or what to use to solve the challenge. May not
       // contain the full address for privacy.
       tan_info: string;
 
     }
 
 Requesting challenges
 ^^^^^^^^^^^^^^^^^^^^^
 
 .. http:post:: [/instances/$INSTANCE]/challenge/$CHALLENGE_ID
 
   Send TAN code for the ``CHALLENGE_ID`` challenge.
 
   This request can be posted several times to trigger TAN retransmission when
   the current code has expired or too many confirmation attempts have been
   made.
 
   This endpoint is not authenticated, it may be used even when mandatory TAN
   channels were not validated yet.
 
   @since **v21**
 
   **Request:**
 
   The request body must be a JSON object, but can otherwise be empty
   (so just send '{}').
 
   **Response:**
 
   :http:statuscode:`200 Ok`:
     The TAN code has been sent. The body will be a `ChallengeRequestResponse`.
   :http:statuscode:`404 Not Found`:
     The challenge was not found.
     Returned with ``TALER_EC_MERCHANT_TAN_CHALLENGE_UNKNOWN``.
   :http:statuscode:`410 Gone`:
     The challenge was already solved.
     Returned with ``TALER_EC_MERCHANT_TAN_CHALLENGE_SOLVED``.
   :http:statuscode:`429 Too many requests`:
     Too many challenges are active right now,
     you must wait or confirm current challenges.
     Returned with ``TALER_EC_MERCHANT_TAN_TOO_EARLY``.
   :http:statuscode:`502 Bad Gateway`:
     TAN transmition via ``tan_channel`` failed.
     Returned with ``TALER_EC_MERCHANT_MFA_HELPER_EXEC_FAILED``.
 
   **Details:**
 
   .. ts:def:: ChallengeRequestResponse
 
     interface ChallengeRequestResponse {
       // How long does the client have to solve the
       // challenge.
       solve_expiration: Timestamp;
 
       // What is the earlist time at which the client
       // may request a new challenge to be transmitted?
       earliest_retransmission: Timestamp;
     }
 
 Solving challenges
 ^^^^^^^^^^^^^^^^^^
 
 .. http:post:: [/instances/$INSTANCE]/challenge/$CHALLENGE_ID/confirm
 
   Solves the ``CHALLENGE_ID`` challenge and allows performing the protected operation.
 
   @since **v21**
 
   When the challenge is confirmed, you can call the protected endpoint again
   with ``CHALLENGE_ID`` in the ``Taler-Challenge-Ids`` HTTP header and the
   original request body.
 
   This endpoints is not authenticated for token creation challenges. Too many
   unsuccessful attempts to confirm token creation challenges block the
   account.
 
   This endpoint may be used even when mandatory TAN channels
   were not validated yet.
 
   **Request:**
 
   .. ts:def:: MerchantChallengeSolveRequest
 
     interface MerchantChallengeSolveRequest {
 
       // The TAN code that solves $CHALLENGE_ID.
       tan: string;
     }
 
   **Response:**
 
   :http:statuscode:`204 No Content`:
     The challenge was solved.
   :http:statuscode:`404 Not Found`:
     The challenge was not found.
     Returned with ``TALER_EC_MERCHANT_TAN_CHALLENGE_UNKNOWN``.
   :http:statuscode:`409 Conflict`:
     Wrong TAN, returned with an
     error code of ``TALER_EC_MERCHANT_TAN_CHALLENGE_FAILED``.
   :http:statuscode:`429 Too many requests`:
     Too many failed confirmation attempts, a new TAN must be requested.
     Returned with ``TALER_EC_MERCHANT_TAN_TOO_MANY_ATTEMPTS``.
 
 ----------
 Wallet API
 ----------
 
 This section describes (public) endpoints that wallets must be able
 to interact with directly (without HTTP-based authentication). These
 endpoints are used to process payments (claiming an order, paying
 for the order, checking payment/refund status and aborting payments),
 and to process refunds (checking refund status, obtaining the refund).
 
 
 Claiming an order
 ^^^^^^^^^^^^^^^^^
 
 The first step of processing any Taler payment consists of the
 (authorized) wallet claiming the order for itself. In this process,
 the wallet provides a wallet-generated nonce that is added
 into the contract terms.  This step prevents two different
 wallets from paying for the same contract, which would be bad
 especially if the merchant only has finite stocks.
 
 A claim token can be used to ensure that the wallet claiming an
 order is actually authorized to do so. This is useful in cases
 where order IDs are predictable and malicious actors may try to
 claim orders (say in a case where stocks are limited).
 
 
 .. http:post:: [/instances/$INSTANCE]/orders/$ORDER_ID/claim
 
   Wallet claims ownership (via nonce) over an order.  By claiming
   an order, the wallet obtains the full contract terms, and thereby
   implicitly also the hash of the contract terms it needs for the
   other ``public`` APIs to authenticate itself as the wallet that
   is indeed eligible to inspect this particular order's status.
 
   **Request:**
 
   The request must be a `ClaimRequest`.
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The client has successfully claimed the order.
     The response contains the :ref:`contract terms <contract-terms>`.
   :http:statuscode:`404 Not found`:
     The backend is unaware of the instance or order.
   :http:statuscode:`409 Conflict`:
     Someone else has already claimed the same order ID with a different nonce.
 
   **Details:**
 
   .. ts:def:: ClaimRequest
 
     interface ClaimRequest {
       // Nonce to identify the wallet that claimed the order.
       nonce: string;
 
       // Token that authorizes the wallet to claim the order.
       // *Optional* as the merchant may not have required it
       // (``create_token`` set to ``false`` in `PostOrderRequest`).
       token?: ClaimToken;
     }
 
   .. ts:def:: ClaimResponse
 
     interface ClaimResponse {
       // Contract terms of the claimed order
       contract_terms: ContractTerms;
 
       // Signature by the merchant over the contract terms.
       sig: EddsaSignature;
     }
 
 Making the payment
 ^^^^^^^^^^^^^^^^^^
 
 .. http:post:: [/instances/$INSTANCE]/orders/$ORDER_ID/pay
 
   Pay for an order by giving a deposit permission for coins.  Typically used by
   the customer's wallet.  Note that this request does not include the
   usual ``h_contract`` argument to authenticate the wallet, as the hash of
   the contract is implied by the signatures of the coins.  Furthermore, this
   API doesn't really return useful information about the order.
 
   **Request:**
 
   The request must be a `pay request <PayRequest>`.
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The exchange accepted all of the coins.
     The body is a `payment response <PaymentResponse>`.
     The ``frontend`` should now fulfill the contract.
     Note that it is possible that refunds have been granted.
   :http:statuscode:`400 Bad request`:
     Either the client request is malformed or some specific processing error
     happened that may be the fault of the client as detailed in the JSON body
     of the response.
     This includes the case where the payment is insufficient (sum is below
     the required total amount, for example because the wallet calculated the
     fees wrong).
 
     Applicable error codes:
 
     * ``MERCHANT_POST_ORDERS_ID_PAY_DENOMINATION_KEY_NOT_FOUND``: Wallet tried
       to pay with a non-existent denomination.
 
   :http:statuscode:`402 Payment required`:
     There used to be a sufficient payment, but due to refunds the amount effectively
     paid is no longer sufficient. (If the amount is generally insufficient, we
     return "400 Bad Request", only if this is because of refunds we return 402.)
   :http:statuscode:`403 Forbidden`:
     One of the coin signatures was not valid.
   :http:statuscode:`404 Not found`:
     The merchant backend could not find the order or the instance and thus cannot process the payment.
   :http:statuscode:`408 Request timeout`:
     The backend took too long to process the request. Likely the merchant's connection
     to the exchange timed out. Try again.
   :http:statuscode:`409 Conflict`:
     The exchange rejected the payment because a coin was already spent (or
     used in a different way for the same purchase previously), or
     the merchant rejected the payment because the order was already fully paid
     (and then return signatures with refunds). If a coin was already spent
     (this includes re-using the same coin after a refund),
     the response will include the ``exchange_url`` for which the payment failed,
     in addition to the response from the exchange to the ``/batch-deposit`` request.
 
     Applicable error codes:
 
     * ``MERCHANT_POST_ORDERS_ID_PAY_INSUFFICIENT_FUNDS``:  Exchange reported insufficient
       funds for one of the coins.
 
   :http:statuscode:`410 Gone`:
     The offer has expired and is no longer available.
   :http:statuscode:`412 Precondition failed`:
     The given exchange is not acceptable for this merchant, as it is not in the
     list of accepted exchanges and not audited by an approved auditor.
     TODO: Status code may be changed to 409 in the future as 412 is technically wrong.
   :http:statuscode:`451 Unavailable for Legal Reasons`:
     The exchange has rejected the deposit by the merchant
     for legal reasons. This is **not** exactly a client
     failure (and possibly nobody's fault except for the
     regulator). In any case, the wallet should refresh
     the deposited coins of the affected exchange and
     may try to pay with coins from another exchange if
     possible (it has such coins and the merchant accepts
     coins from another exchange).
     The body is a `PaymentDeniedLegallyResponse` with
     details about the failure.
     Since protocol **v17**.
   :http:statuscode:`502 Bad gateway`:
     The merchant's interaction with the exchange failed in some way.
     The client might want to try again later.
     This includes failures such as the denomination key of a coin not being
     known to the exchange as far as the merchant can tell.
   :http:statuscode:`504 Gateway timeout`:
     The merchant's interaction with the exchange took too long.
     The client might want to try again later.
 
   The backend will return verbatim the error codes received from the exchange's
   :ref:`deposit <deposit>` API.  If the wallet made a mistake, like by
   double-spending for example, the frontend should pass the reply verbatim to
   the browser/wallet.  If the payment was successful, the frontend MAY use
   this to trigger some business logic.
 
   **Details:**
 
   .. ts:def:: PaymentResponse
 
     interface PaymentResponse {
       // Signature on ``TALER_PaymentResponsePS`` with the public
       // key of the merchant instance.
       sig: EddsaSignature;
 
       // Text to be shown to the point-of-sale staff as a proof of
       // payment.
       pos_confirmation?: string;
 
       // Signed tokens. Returned in the same order as the
       // token envelopes were provided in the request. Specifically,
       // the order will follow the order of the outputs from the
       // contract terms, and then within each output follow the
       // order in which the ``wallet_data`` contained the respective
       // blinded envelopes.  The donation tokens will be present
       // at the offset matching the place where a donation receipt
       // was indicated in the outputs array, and of course be skipped
       // if the ``PayWalletData`` did not have a ``donau`` field.
       // @since protocol **v21**
       token_sigs?: SignedTokenEnvelope[];
 
     }
 
   .. ts:def:: PayRequest
 
     interface PayRequest {
       // The coins used to make the payment.
       coins: CoinPaySig[];
 
       // Input tokens required by choice indicated by ``choice_index``.
       // @since protocol **v21**
       tokens?: TokenUseSig[];
 
       // Custom inputs from the wallet for the contract.
       wallet_data?: PayWalletData;
 
       // The session for which the payment is made (or replayed).
       // Only set for session-based payments.
       session_id?: string;
 
     }
 
   .. ts:def:: SignedTokenEnvelope
 
     interface SignedTokenEnvelope {
 
       // Blind signature made by the merchant.
       blind_sig: TokenIssueBlindSig;
 
     }
 
   .. ts:def:: TokenIssueBlindSig
 
     type TokenIssueBlindSig = RSATokenIssueBlindSig | CSTokenIssueBlindSig;
 
   .. ts:def:: RSATokenIssueBlindSig
 
     interface RSATokenIssueBlindSig {
       cipher: "RSA";
 
       // (blinded) RSA signature
       blinded_rsa_signature: BlindedRsaSignature;
     }
 
   .. ts:def:: CSTokenIssueBlindSig
 
     interface CSTokenIssueBlindSig {
       cipher: "CS";
 
       // Signer chosen bit value, 0 or 1, used
       // in Clause Blind Schnorr to make the
       // ROS problem harder.
       b: Integer;
 
       // Blinded scalar calculated from c_b.
       s: Cs25519Scalar;
 
     }
 
   .. ts:def:: PayWalletData
 
     interface PayWalletData {
       // Index of the selected choice within the ``choices`` array of
       // the contract terms.
       // @since protocol **v21**
       choice_index?: Integer;
 
       // Array of output tokens to be (blindly) signed by the merchant.
       // Output tokens specified in choice indicated by ``choice_index``.
       // @since protocol **v21**
       tokens_evs?: TokenEnvelope[];
 
       // Request for donation receipts to be issued.
       // @since protocol **v21**
       donau?: DonationRequestData;
     }
 
   .. ts:def:: DonationRequestData
 
     interface DonationRequestData {
       // Base URL of the selected Donau
       url: string;
 
       // Year for which the donation receipts are expected.
       // Also determines which keys are used to sign the
       // blinded donation receipts.
       year: Integer;
 
       // Array of blinded donation receipts to sign.
       // Must NOT be empty (if no donation receipts
       // are desired, just leave the entire ``donau``
       // argument blank).
       budikeypairs: BlindedDonationReceiptKeyPair[];
     }
 
   .. ts:def:: CoinPaySig
 
     interface CoinPaySig {
       // Signature by the coin.
       coin_sig: EddsaSignature;
 
       // Public key of the coin being spent.
       coin_pub: EddsaPublicKey;
 
       // Signature made by the denomination public key.
       ub_sig: UnblindedSignature;
 
       // The hash of the denomination public key associated with this coin.
       h_denom: HashCode;
 
       // The amount that is subtracted from this coin with this payment.
       contribution: Amount;
 
       // URL of the exchange this coin was withdrawn from.
       exchange_url: string;
 
       // Signature affirming the posession of the
       // respective private key proving that the payer
       // is old enough. Only provided if the paid contract
       // has an age restriction and the coin is
       // age-restricted.
       minimum_age_sig?: EddsaSignature;
 
       // Age commitment vector of the coin.
       // Only provided if the paid contract
       // has an age restriction and the coin is
       // age-restricted.
       age_commitment?: Edx25519PublicKey[];
 
       // Hash over the agge commitment vector of the coin.
       // Only provided if the paid contract
       // does NOT have an age restriction and the coin is
       // age-restricted.
       h_age_commitment?: AgeCommitmentHash;
     }
 
   .. ts:def:: TokenUseSig
 
     interface TokenUseSig {
 
       // Signature on ``TALER_TokenUseRequestPS`` with the token use key of
       // the token being used in this request.
       token_sig: EddsaSignature;
 
       // Token use public key.
       token_pub: EddsaPublicKey;
 
       // Unblinded signature on ``TALER_TokenIssueRequestPS`` with the token
       // issue public key of the merchant.
       ub_sig: UnblindedSignature;
 
       // Hash of the token issue public key associated with this token.
       h_issue: HashCode;
     }
 
   .. ts:def:: TokenEnvelope
 
     // This type depends on the cipher used to sign token families. This is
     // configured by the merchant and defined for each token family in the
     // contract terms.
     type TokenEnvelope = RSATokenEnvelope | CSTokenEnvelope;
 
   .. ts:def:: RSATokenEnvelope
 
     interface RSATokenEnvelope {
 
       // RSA is used for the blind signature.
       cipher: "RSA";
 
       // Blinded signature of the token's `public EdDSA key <eddsa-token-pub>`.
       rsa_blinded_pub: BlindedRsaSignature;
 
     }
 
   .. ts:def:: CSTokenEnvelope
 
     interface CSTokenEnvelope {
       // Blind Clause-Schnorr signature scheme is used for the blind signature.
       // See https://taler.net/papers/cs-thesis.pdf for details.
       cipher: "CS";
 
       // Public nonce
       cs_nonce: string;      // Crockford `Base32` encoded
 
       // Two Curve25519 scalars, each representing a blinded challenge
       cs_blinded_c0: string; // Crockford `Base32` encoded
       cs_blinded_c1: string; // Crockford `Base32` encoded
     }
 
   .. ts:def:: PaymentDeniedLegallyResponse
 
     interface PaymentDeniedLegallyResponse {
 
        // Base URL of the exchanges that denied the payment.
        // The wallet should refresh the coins from these
        // exchanges, but may try to pay with coins from
        // other exchanges.
        exchange_base_urls: string[];
 
     }
 
 
 Querying payment status
 ^^^^^^^^^^^^^^^^^^^^^^^
 
 .. http:get:: [/instances/$INSTANCE]/orders/$ORDER_ID
 
   Query the payment status of an order. This endpoint is for the wallet
   and possibly for Web shops and other integrations that need an
   unauthenticated way to query the order status (like when checking
   it from JavaScript from inside the customer's browser). It is also
   possible to just redirect a browser to this URL to initiate the
   payment process.
 
   When a client (usually a wallet) goes to this URL and it is unpaid,
   it will be prompted for payment.
   This endpoint typically also supports requests with the "Accept" header
   requesting "text/html".  In this case, an HTML response suitable for
   triggering the interaction with the wallet is returned, with ``timeout_ms``
   ignored (treated as zero). If the backend installation does not include the
   required HTML templates, a 406 status code is returned.
 
   In the case that the request was made with a claim token (even the wrong one)
   and the order was claimed and paid, the server will redirect the client to
   the fulfillment URL.  This redirection will happen with a 302 status code
   if the "Accept" header specified "text/html", and with a 202 status code
   otherwise.
 
   **Request:**
 
   :query h_contract=HASH: *Optional*. Hash of the order's contract terms (this is used to authenticate the wallet/customer in case $ORDER_ID is guessable). Required once an order was claimed.
   :query token=TOKEN: *Optional*. Authorizes the request via the claim token that was returned in the `PostOrderResponse`.  Used with unclaimed orders only. Whether token authorization is required is determined by the merchant when the frontend creates the order.
   :query session_id=STRING: *Optional*. Session ID that the payment must be bound to.  If not specified, the payment is not session-bound.
   :query timeout_ms=NUMBER: *Optional.*  If specified, the merchant backend will
     wait up to ``timeout_ms`` milliseconds for completion of the payment before
     sending the HTTP response.  A client must never rely on this behavior, as the
     merchant backend may return a response immediately.
   :query await_refund_obtained=BOOLEAN: *Optional*. If set to "yes", poll for the order's pending refunds to be picked up.  ``timeout_ms`` specifies how long we will wait for the refund.
   :query refund=AMOUNT: *Optional*. Indicates that we are polling for a refund above the given AMOUNT. ``timeout_ms`` will specify how long we will wait for the refund.
   :query allow_refunded_for_repurchase: *Optional*. Since protocol **v9** refunded orders are only returned under "already_paid_order_id" if this flag is set explicitly to "YES".
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The response is a `StatusPaidResponse`.
   :http:statuscode:`202 Accepted`:
     The response is a `StatusGotoResponse`. Only returned if the content type requested was not HTML.
     The target site may allow the client to setup a fresh order (as this one has been taken) or may
     trigger repurchase detection.
   :http:statuscode:`302 Found`:
     The client should go to the indicated location (via HTTP "Location:" header).
     Only returned if the content type requested was HTML.
     The target site may allow the client to setup a fresh order (as this one has been taken) or may
     trigger repurchase detection.
   :http:statuscode:`402 Payment required`:
     The response is a `StatusUnpaidResponse`.
   :http:statuscode:`403 Forbidden`:
     The ``h_contract`` (or the ``token`` for unclaimed orders) does not match the order
     and we have no fulfillment URL in the contract.
   :http:statuscode:`404 Not found`:
     The merchant backend is unaware of the order.
   :http:statuscode:`406 Not acceptable`:
     The merchant backend could not load the template required to generate a reply in the desired format. (Likely HTML templates were not properly installed.)
 
   **Details:**
 
   .. ts:def:: StatusPaidResponse
 
     interface StatusPaidResponse {
       // Was the payment refunded (even partially, via refund or abort)?
       refunded: boolean;
 
       // Is any amount of the refund still waiting to be picked up (even partially)?
       refund_pending: boolean;
 
       // Amount that was refunded in total.
       refund_amount: Amount;
 
       // Amount that already taken by the wallet.
       refund_taken: Amount;
     }
 
   .. ts:def:: StatusGotoResponse
 
     interface StatusGotoResponse {
       // The client should go to the reorder URL, there a fresh
       // order might be created as this one is taken by another
       // customer or wallet (or repurchase detection logic may
       // apply).
       public_reorder_url: string;
     }
 
   .. ts:def:: StatusUnpaidResponse
 
     interface StatusUnpaidResponse {
       // URI that the wallet must process to complete the payment.
       taler_pay_uri: string;
 
       // Fulfillment URL of the contract.
       // If present, it should be possible to create an
       // equivalent order by redirecting a browser to this
       // URL. Once the customer has paid, they should see the
       // order's fulfillment (digital goods, tracking data for
       // shipping, etc.) under this URL (assuming they use the
       // same session that the wallet used when making the payment).
       fulfillment_url?: string;
 
       // Alternative order ID which was paid for already in the same session.
       // Only given if the same product was purchased before in the same session.
       already_paid_order_id?: string;
     }
 
 
 
 Demonstrating payment
 ^^^^^^^^^^^^^^^^^^^^^
 
 In case a wallet has already paid for an order, this is a fast way of proving
 to the merchant that the order was already paid. The alternative would be to
 replay the original payment, but simply providing the merchant's signature
 saves bandwidth and computation time.
 
 Demonstrating payment is useful in case a digital good was made available
 only to clients with a particular session ID: if that session ID expired or
 if the user is using a different client, demonstrating payment will allow
 the user to regain access to the digital good without having to pay for it
 again.
 
 .. http:post:: [/instances/$INSTANCE]/orders/$ORDER_ID/paid
 
   Prove that the client previously paid for an order by providing
   the merchant's signature from the `payment response <PaymentResponse>`.
   Typically used by the customer's wallet if it receives a request for
   payment for an order that it already paid. This is more compact than
   re-transmitting the full payment details.
   Note that this request does include the
   usual ``h_contract`` argument to authenticate the wallet and
   to allow the merchant to verify the signature before checking
   with its own database.
 
   **Request:**
 
   The request must be a `paid request <PaidRequest>`.
 
   **Response:**
 
   :http:statuscode:`200 Ok`:
     The merchant accepted the signature.
     The ``frontend`` should now fulfill the contract.
     Note that it is possible that refunds have been granted.  Response is of type `PaidRefundStatusResponse`.
   :http:statuscode:`400 Bad request`:
     Either the client request is malformed or some specific processing error
     happened that may be the fault of the client as detailed in the JSON body
     of the response.
   :http:statuscode:`403 Forbidden`:
     The signature was not valid.
   :http:statuscode:`404 Not found`:
     The merchant backend could not find the order or the instance
     and thus cannot process the request.
 
   **Details**:
 
   .. ts:def:: PaidRefundStatusResponse
 
     interface PaidRefundStatusResponse {
 
       // Text to be shown to the point-of-sale staff as a proof of
       // payment (present only if re-usable OTP algorithm is used).
       pos_confirmation?: string;
 
       // True if the order has been subjected to
       // refunds. False if it was simply paid.
       refunded: boolean;
     }
 
   .. ts:def:: PaidRequest
 
     interface PaidRequest {
       // Signature on ``TALER_PaymentResponsePS`` with the public
       // key of the merchant instance.
       sig: EddsaSignature;
 
       // Hash of the order's contract terms (this is used to authenticate the
       // wallet/customer and to enable signature verification without
       // database access).
       h_contract: HashCode;
 
       // Session id for which the payment is proven.
       session_id: string;
     }
 
 
 Aborting incomplete payments
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 In rare cases (such as a wallet restoring from an outdated backup) it is possible
 that a wallet fails to complete a payment because it runs out of e-cash in the
 middle of the process. The abort API allows the wallet to abort the payment for
 such an incomplete payment and to regain control over the coins that were spent
 so far. Aborts are not permitted for payments that have completed.  In contrast to
 refunds, aborts do not require approval by the merchant because aborts always
 are for incomplete payments for an order and never for established contracts.
 
 
 .. _order-abort:
 .. http:post:: [/instances/$INSTANCE]/orders/$ORDER_ID/abort
 
   Abort paying for an order and obtain a refund for coins that
   were already deposited as part of a failed payment.
 
   **Request:**
 
   The request must be an `abort request <AbortRequest>`.  We force the wallet
   to specify the affected coins as it may only request for a subset of the coins
   (i.e. because the wallet knows that some were double-spent causing the failure).
   Also we need to know the coins because there may be two wallets "competing" over
   the same order and one wants to abort while the other still proceeds with the
   payment. Here we need to again know which subset of the deposits to abort.
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The merchant accepted the request, and passed it on to the exchange. The body is a
     a `abort response <AbortResponse>`. Note that the exchange
     MAY still have encountered errors in processing. Those will then be part of
     the body. Wallets MUST carefully consider errors for each of the coins as
     returned by the exchange.
   :http:statuscode:`400 Bad request`:
     Either the client request is malformed or some specific processing error
     happened that may be the fault of the client as detailed in the JSON body
     of the response.
   :http:statuscode:`403 Forbidden`:
     The ``h_contract`` does not match the $ORDER_ID.
   :http:statuscode:`404 Not found`:
     The merchant backend could not find the order or the instance
     and thus cannot process the abort request.
   :http:statuscode:`408 Request timeout`:
     The merchant backend took too long getting a response from the exchange.
     The wallet SHOULD retry soon.
   :http:statuscode:`412 Precondition failed`:
     Aborting the payment is not allowed, as the original payment did succeed.
     It is possible that a different wallet succeeded with the payment. This
     wallet should thus try to refresh all of the coins involved in the payment.
   :http:statuscode:`502 Bad gateway`:
     The merchant's interaction with the exchange failed in some way.
     The error from the exchange is included.
   :http:statuscode:`504 Gateway timeout`:
     The merchant's interaction with the exchange took too long.
     The client might want to try again later.
 
   The backend will return an `abort response <AbortResponse>`, which includes
   verbatim the error codes received from the exchange's
   :ref:`refund <exchange_refund>` API.  The frontend should pass the replies verbatim to
   the browser/wallet.
 
   **Details:**
 
   .. ts:def:: AbortRequest
 
     interface AbortRequest {
 
       // Hash of the order's contract terms (this is used to authenticate the
       // wallet/customer in case $ORDER_ID is guessable).
       h_contract: HashCode;
 
       // List of coins the wallet would like to see refunds for.
       // (Should be limited to the coins for which the original
       // payment succeeded, as far as the wallet knows.)
       coins: AbortingCoin[];
     }
 
   .. ts:def:: AbortingCoin
 
     interface AbortingCoin {
       // Public key of a coin for which the wallet is requesting an abort-related refund.
       coin_pub: EddsaPublicKey;
 
       // The amount to be refunded (matches the original contribution)
       // @Deprecated since **v18**.
       contribution: Amount;
 
       // URL of the exchange this coin was withdrawn from.
       exchange_url: string;
     }
 
 
   .. ts:def:: AbortResponse
 
     interface AbortResponse {
 
       // List of refund responses about the coins that the wallet
       // requested an abort for.  In the same order as the ``coins``
       // from the original request.
       // The ``rtransaction_id`` is implied to be 0.
       refunds: MerchantAbortPayRefundStatus[];
     }
 
   .. ts:def:: MerchantAbortPayRefundStatus
 
     type MerchantAbortPayRefundStatus =
       | MerchantAbortPayRefundSuccessStatus
       | MerchantAbortPayRefundUndepositedStatus
       | MerchantAbortPayRefundFailureStatus;
 
   .. ts:def:: MerchantAbortPayRefundFailureStatus
 
     // Details about why a refund failed.
     interface MerchantAbortPayRefundFailureStatus {
       // Used as tag for the sum type RefundStatus sum type.
       type: "failure";
 
       // HTTP status of the exchange request, must NOT be 200.
       exchange_status: Integer;
 
       // Taler error code from the exchange reply, if available.
       exchange_code?: Integer;
 
       // If available, HTTP reply from the exchange.
       exchange_reply?: Object;
     }
 
   .. ts:def:: MerchantAbortPayRefundSuccessStatus
 
     // Additional details needed to verify the refund confirmation signature
     // (``h_contract_terms`` and ``merchant_pub``) are already known
     // to the wallet and thus not included.
     interface MerchantAbortPayRefundSuccessStatus {
       // Used as tag for the sum type MerchantCoinRefundStatus sum type.
       type: "success";
 
       // HTTP status of the exchange request, 200 (integer) required for refund confirmations.
       exchange_status: 200;
 
       // The EdDSA :ref:`signature` (binary-only) with purpose
       // `TALER_SIGNATURE_EXCHANGE_CONFIRM_REFUND` using a current signing key of the
       // exchange affirming the successful refund.
       exchange_sig: EddsaSignature;
 
       // Public EdDSA key of the exchange that was used to generate the signature.
       // Should match one of the exchange's signing keys from ``/keys``.  It is given
       // explicitly as the client might otherwise be confused by clock skew as to
       // which signing key was used.
       exchange_pub: EddsaPublicKey;
     }
 
   .. ts:def:: MerchantAbortPayRefundUndepositedStatus
 
     // The merchant didn't deposit the coin in the first place,
     // no refund possible.
     interface MerchantAbortPayRefundSuccessStatus {
       // Used as tag for the sum type MerchantCoinRefundStatus sum type.
       type: "undeposited";
     }
 
 
 Obtaining refunds
 ^^^^^^^^^^^^^^^^^
 
 Refunds allow merchants to fully or partially restitute e-cash to a wallet,
 for example because the merchant determined that it could not actually fulfill
 the contract. Refunds must be approved by the merchant's business logic.
 
 
 .. http:post:: [/instances/$INSTANCE]/orders/$ORDER_ID/refund
 
   Obtain refunds for an order. After talking to the exchange, the refunds will
   no longer be pending if processed successfully.
 
   **Request:**
 
   The request body is a `WalletRefundRequest` object.
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The response is a `WalletRefundResponse`.
   :http:statuscode:`204 No content`:
     There are no refunds for the order.
   :http:statuscode:`403 Forbidden`:
     The ``h_contract`` does not match the order.
   :http:statuscode:`404 Not found`:
     The merchant backend is unaware of the order.
   :http:statuscode:`410 Gone`:
     The wire deadline has past and it is too late to grant a refund.
     Since protocol **v24**.
   :http:statuscode:`451 Unavailable for Legal Reasons`:
     The refund could not be awarded because of legal
     reasons (an exchange refused). The wallet should
     show an error message and suggest to the user to
     get in touch with the merchant to try to get the
     refund in a different way.
     The body is a `PaymentDeniedLegallyResponse` with
     details about the exchange causing the failure.
     Since protocol **v17**.
 
   **Details:**
 
   .. ts:def:: WalletRefundRequest
 
     interface WalletRefundRequest {
       // Hash of the order's contract terms (this is used to authenticate the
       // wallet/customer).
       h_contract: HashCode;
     }
 
   .. ts:def:: WalletRefundResponse
 
     interface WalletRefundResponse {
       // Amount that was refunded in total.
       refund_amount: Amount;
 
       // Successful refunds for this payment, empty array for none.
       refunds: MerchantCoinRefundStatus[];
 
       // Public key of the merchant.
       merchant_pub: EddsaPublicKey;
 
     }
 
   .. ts:def:: MerchantCoinRefundStatus
 
     type MerchantCoinRefundStatus =
       | MerchantCoinRefundSuccessStatus
       | MerchantCoinRefundFailureStatus;
 
   .. ts:def:: MerchantCoinRefundFailureStatus
 
     // Details about why a refund failed.
     interface MerchantCoinRefundFailureStatus {
       // Used as tag for the sum type RefundStatus sum type.
       type: "failure";
 
       // HTTP status of the exchange request, must NOT be 200.
       exchange_status: Integer;
 
       // Taler error code from the exchange reply, if available.
       exchange_code?: Integer;
 
       // If available, HTTP reply from the exchange.
       exchange_reply?: Object;
 
       // Refund transaction ID.
       rtransaction_id: Integer;
 
       // Public key of a coin that was refunded.
       coin_pub: EddsaPublicKey;
 
       // Amount that was refunded, including refund fee charged by the exchange
       // to the customer.
       refund_amount: Amount;
 
       // Timestamp when the merchant approved the refund.
       // Useful for grouping refunds.
       execution_time: Timestamp;
     }
 
   .. ts:def:: MerchantCoinRefundSuccessStatus
 
     // Additional details needed to verify the refund confirmation signature
     // (``h_contract_terms`` and ``merchant_pub``) are already known
     // to the wallet and thus not included.
     interface MerchantCoinRefundSuccessStatus {
       // Used as tag for the sum type MerchantCoinRefundStatus sum type.
       type: "success";
 
       // HTTP status of the exchange request, 200 (integer) required for refund confirmations.
       exchange_status: 200;
 
       // The EdDSA :ref:`signature` (binary-only) with purpose
       // `TALER_SIGNATURE_EXCHANGE_CONFIRM_REFUND` using a current signing key of the
       // exchange affirming the successful refund.
       exchange_sig: EddsaSignature;
 
       // Public EdDSA key of the exchange that was used to generate the signature.
       // Should match one of the exchange's signing keys from /keys.  It is given
       // explicitly as the client might otherwise be confused by clock skew as to
       // which signing key was used.
       exchange_pub: EddsaPublicKey;
 
       // Refund transaction ID.
       rtransaction_id: Integer;
 
       // Public key of a coin that was refunded.
       coin_pub: EddsaPublicKey;
 
       // Amount that was refunded, including refund fee charged by the exchange
       // to the customer.
       refund_amount: Amount;
 
       // Timestamp when the merchant approved the refund.
       // Useful for grouping refunds.
       execution_time: Timestamp;
     }
 
 
 -------------------
 Instance management
 -------------------
 
 Instances allow one merchant backend to be shared by multiple merchants.
 Every backend must have at least one instance, typically the "admin"
 instance setup before it can be used to manage inventory or process payments.
 
 
 Setting up instances
 ^^^^^^^^^^^^^^^^^^^^
 
 .. http:post:: /instances
 
   This request will be used to create a new merchant instance in the backend.
   Since protocol **v21**.
 
   Only available if self-provisioning is enabled.
 
   **Required permission:** none
 
   **Request:**
 
   The request must be a `InstanceConfigurationMessage`.
 
   :query token_validity_ms=DURATION: *Optional*.
     Pass a non-zero DURATION in milliseconds to get a
     refreshable login token for the SPA with the
     given validity duration in the response.  @since **v21**.
 
   **Response:**
 
   :http:statuscode:`200 Ok`:
     The backend has successfully created the instance. Body will
     be an `LoginTokenSuccessResponse` with a refreshable
     login token for the SPA as requested. @since **v21**.
   :http:statuscode:`202 Accepted`:
     2FA is required for this operation, usually to validate the
     email and/or phone numbers provided for the instance.
     This returns the `ChallengeResponse`. @since **v21**
   :http:statuscode:`204 No Content`:
     The backend has successfully created the instance. No login
     token was requested, so nothing is returned.
   :http:statuscode:`409 Conflict`:
     This instance already exists, but with other configuration options.
     Use "PATCH" to update an instance configuration. Alternatively,
     the currency provided in the configuration does not match the
     currency supported by this backend. Another possible conflict
     would be if a deleted but not purged instance is known under this
     ID to the backend.
 
 
 .. http:post:: /instances/$INSTANCE/forgot-password
 
   Same as ``/management/instances/$INSTANCE/private/auth`` it will update the password of the instance but
   without requiring the current password. On the first call it will validate the request
   and return the multi-factor authentication challenge IDs with
   a ``202 Accepted`` response. Once the challenges are solved the
   request needs to be repeated with the ``Taler-Challenge-Ids`` header.
 
   This endpoint is **not** available for the ``admin`` instance.
   The administrator must use the command-line tool if they forgot
   their password.
 
   Since protocol **v21**
 
   **Request** the request must be an `InstanceAuthConfigurationMessage`.
 
   **Response:**
 
   :http:statuscode:`202 Accepted`:
     2FA is required for this operation. This returns
     the `ChallengeResponse`. @since **v21**
   :http:statuscode:`204 No content`:
     The backend has successfully changed the credentials for the instance.
   :http:statuscode:`404 Not found`:
     This instance is unknown and thus cannot be reconfigured.
 
 
 .. http:post:: /management/instances
 
   This request will be used to create a new merchant instance in the backend.
   It is only available for the implicit ``admin`` instance.
 
   **Required permission:** ``instances-write``
 
   **Request:**
 
   The request must be a `InstanceConfigurationMessage`.
 
   **Response:**
 
   :http:statuscode:`202 Accepted`:
     2FA is required for this operation, usually to validate the
     email and/or phone numbers registered for the instance.
     This returns the `ChallengeResponse`. @since **v21**
   :http:statuscode:`204 No content`:
     The backend has successfully created the instance.
   :http:statuscode:`409 Conflict`:
     This instance already exists, but with other configuration options.
     Use "PATCH" to update an instance configuration. Alternatively,
     the currency provided in the configuration does not match the
     currency supported by this backend. Another possible conflict
     would be if a deleted but not purged instance is known under this
     ID to the backend.
 
   **Details:**
 
   .. ts:def:: InstanceConfigurationMessage
 
     interface InstanceConfigurationMessage {
 
       // Name of the merchant instance to create (will become $INSTANCE).
       // Must match the regex ``^[A-Za-z0-9][A-Za-z0-9_.@-]+$``.
       id: string;
 
       // Merchant name corresponding to this instance.
       name: string;
 
       // Merchant email for customer contact and password reset.
       email?: string;
 
       // Merchant phone number for password reset (2-FA)
       // @since **v21**.
       phone_number?: string;
 
       // Merchant public website.
       website?: string;
 
       // Merchant logo.
       logo?: ImageDataUrl;
 
       // Authentication settings for this instance
       auth: InstanceAuthConfigurationMessage;
 
       // The merchant's physical address (to be put into contracts).
       address: Location;
 
       // The jurisdiction under which the merchant conducts its business
       // (to be put into contracts).
       jurisdiction: Location;
 
       // Use STEFAN curves to determine default fees?
       // If false, no fees are allowed by default.
       // Can always be overridden by the frontend on a per-order basis.
       use_stefan: boolean;
 
       // If the frontend does NOT specify a payment deadline, how long should
       // offers we make be valid by default?
       // Optional @since **v22** (before the setting was mandatory).
       // If not provided, the global merchant default will be used.
       default_pay_delay?: RelativeTime;
 
       // If the frontend does NOT specify a refund deadline, how long should
       // refunds be allowed by default? Added on top of the
       // payment deadline.
       // @since **v22**
       default_refund_delay?: RelativeTime;
 
       // If the frontend does NOT specify an execution date, how long should
       // we tell the exchange to wait to aggregate transactions before
       // executing the wire transfer?  This delay is added on top of
       // the refund deadline and afterwards subject to rounding
       // via the ``default_wire_transfer_rounding_interval``.
       // Optional @since **v22** (before the setting was mandatory).
       // If not provided, the global merchant default will be used.
       default_wire_transfer_delay?: RelativeTime;
 
       // How far should the wire deadline (if computed with the help of
       // the ``default_wire_transfer_delay``) be rounded up to compute
       // the ultimate wire deadline?
       // @since **v22**, defaults to no rounding if not given.
       default_wire_transfer_rounding_interval?: RoundingInterval;
     }
 
 .. http:post:: /management/instances/$INSTANCE/auth
 .. http:post:: [/instances/$INSTANCE]/private/auth
 
   Update the authentication settings for an instance.  POST operations against
   an instance are authenticated by checking that an authorization is provided
   that matches either the credential required by the instance being modified
   OR the ``admin`` instance, depending on the access path used.
 
   **Required permission:** ``instances-auth-write``
 
   **Request** the request must be an `InstanceAuthConfigurationMessage`.
 
   **Response:**
 
   :http:statuscode:`202 Accepted`:
     2FA is required for this operation. This returns the `ChallengeResponse` response. @since **v21**
   :http:statuscode:`204 No content`:
     The backend has successfully changed the credentials for the instance.
   :http:statuscode:`404 Not found`:
     This instance is unknown and thus cannot be reconfigured.
 
   **Details:**
 
   .. ts:def:: InstanceAuthConfigurationMessage
 
     type InstanceAuthConfigurationMessage = InstanceAuthConfigToken | InstanceAuthConfigTokenOLD | InstanceAuthConfigExternal
 
   .. ts:def:: InstanceAuthConfigToken
 
     // @since **v19**
     interface InstanceAuthConfigToken {
       // The API is accessible through API tokens.
       // Tokens are retrieved from the /private/token
       // endpoint.
       method: "token";
 
       // Authentication against the /private/token endpoint
       // is done using basic authentication with the configured password
       // in the "password" field. Tokens are passed to other endpoints for
       // authorization using RFC 8959 bearer tokens.
       password: string;
 
     }
 
   .. ts:def:: InstanceAuthConfigTokenOLD
 
     // @deprecated since **v19**
     interface InstanceAuthConfigTokenOLD {
       // The API is accessible through API tokens.
       // Tokens are retrieved from the /private/token
       // endpoint.
       method: "token";
 
       // The value of this field MUST begin with the string "secret-token:".
       token: string;
 
     }
 
   .. ts:def:: InstanceAuthConfigExternal
 
     // @deprecated since **v20**
     interface InstanceAuthConfigExternal {
       // The mechant backend does not do
       // any authentication checks.  Instead an API
       // gateway must do the authentication.
       method: "external";
     }
 
 
 .. http:post:: [/instances/$INSTANCE]/private/token
 
   Retrieve an access token for the merchant API for instance
   ``$INSTANCE``.
   When accessed with a Bearer token for authentication, the token
   must have scope ``token-refresh`` and the requested scope must be a subset
   of the scope of the token.
   When accessed with Basic authentication the instance password must be provided
   along with ``$INSTANCE`` as username.
 
 
   **Required permission:** ``token-refresh`` if accessed using a Bearer token.
 
   **Request:**
 
   The request must be a `LoginTokenRequest`.
 
   **Response:**
 
   :http:statuscode:`200 Ok`:
     The backend is returning the access token in a
     `LoginTokenSuccessResponse`.
   :http:statuscode:`202 Accepted`:
     2FA is required for this operation.
     This returns the `ChallengeResponse`. @since **v21**
 
   **Details:**
 
   .. ts:def:: LoginTokenRequest
 
     interface LoginTokenRequest {
       // Scope of the token (which kinds of operations it will allow)
       scope: "readonly" | "write" | "all" | "order-simple" | "order-pos" | "order-mgmt" | "order-full";
 
       // Server may impose its own upper bound
       // on the token validity duration
       duration?: RelativeTime;
 
       // Optional token description
       description?: string;
 
       // Can this token be refreshed?
       // Defaults to false. Deprecated since **v19**.
       // Use ":refreshable" scope prefix instead.
       refreshable?: boolean;
     }
 
   .. ts:def:: LoginTokenSuccessResponse
 
     interface LoginTokenSuccessResponse {
       // deprecated since v19. See access_token
       token: string;
 
       // The login token that can be used to access resources
       // that are in scope for some time. Must be prefixed
       // with "Bearer " when used in the "Authorization" HTTP header.
       // Will already begin with the RFC 8959 prefix.
       // **Since v19**
       access_token: string;
 
       // Scope of the token (which kinds of operations it will allow)
       scope: "readonly" | "write" | "all" | "order-simple" | "order-pos" | "order-mgmt" | "order-full";
 
       // Server may impose its own upper bound
       // on the token validity duration
       expiration: Timestamp;
 
       // Can this token be refreshed?
       refreshable: boolean;
     }
 
 .. http:get:: [/instances/$INSTANCE]/private/tokens
 
   Retrieve a list of issued access tokens for ``$INSTANCE``.
 
   @since **v19**
 
   **Required permission**: ``tokens-read``
 
   **Request:**
 
   :query limit: *Optional.*
     At most return the given number of results. Negative for descending by ``serial``, positive for ascending by ``serial``. Defaults to ``-20``.
   :query offset: *Optional.*
     Starting ``serial`` for :ref:`pagination <row-id-pagination>`.
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     Response is a `TokenInfos`.
   :http:statuscode:`204 No content`:
     No tokens.
   :http:statuscode:`401 Unauthorized`:
     Invalid or missing credentials.
   :http:statuscode:`403 Forbidden`:
     Missing rights.
 
   **Details:**
 
   .. ts:def:: TokenInfos
 
     interface TokenInfos {
       tokens: TokenInfo[];
     }
 
   .. ts:def:: TokenInfo
 
     interface TokenInfo {
       // Time when the token was created.
       creation_time: Timestamp;
 
       // Time when the token expires.
       expiration: Timestamp;
 
       // Scope for the token.
       scope: "readonly" | "readwrite" | ...;
 
       // Is the token refreshable into a new token during its
       // validity?
       // Refreshable tokens effectively provide indefinite
       // access if they are refreshed in time.
       refreshable: boolean;
 
       // Optional token description
       description?: string;
 
       // Opaque unique ID used for pagination.
       serial: Integer;
     }
 
 .. http:delete:: [/instances/$INSTANCE]/private/tokens/$SERIAL
 
   Delete a token for ``$INSTANCE`` API access by its ``$SERIAL``.
 
 
   @since **v19**
 
   **Required permission**: ``tokens-write``
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     Token deleted.
   :http:statuscode:`401 Unauthorized`:
     Invalid or missing credentials.
   :http:statuscode:`403 Forbidden`:
     Missing permission.
   :http:statuscode:`404 Not found`:
     The token was not found.
 
 .. http:delete:: [/instances/$INSTANCE]/private/token
 
    Delete the token presented in the authorization header.
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The access token used to authorize this request was revoked.
 
 .. http:patch:: /management/instances/$INSTANCE
 .. http:patch:: [/instances/$INSTANCE]/private
 
   Update the configuration of a merchant instance.  PATCH operations against
   an instance are authenticated by checking that an authorization is provided
   that matches either the credential required by the instance being modified
   OR the ``admin`` instance, depending on the access path used.
 
   **Required permission:** ``instances-token-write``
 
   **Request**
 
   The request must be a `InstanceReconfigurationMessage`.
   Removing an existing ``payto_uri`` deactivates
   the account (it will no longer be used for future contracts).
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The backend has successfully created the instance.
   :http:statuscode:`404 Not found`:
     This instance is unknown and thus cannot be reconfigured.
 
   **Details:**
 
   .. ts:def:: InstanceReconfigurationMessage
 
     interface InstanceReconfigurationMessage {
 
       // Merchant name corresponding to this instance.
       name: string;
 
       // Merchant email for customer contact and password reset.
       email?: string;
 
       // Merchant phone number for password reset (2-FA)
       // @since **v21**.
       phone_number?: string;
 
       // Merchant public website.
       website?: string;
 
       // Merchant logo.
       logo?: ImageDataUrl;
 
       // The merchant's physical address (to be put into contracts).
       address: Location;
 
       // The jurisdiction under which the merchant conducts its business
       // (to be put into contracts).
       jurisdiction: Location;
 
       // Use STEFAN curves to determine default fees?
       // If false, no fees are allowed by default.
       // Can always be overridden by the frontend on a per-order basis.
       use_stefan: boolean;
 
       // If the frontend does NOT specify a payment deadline, how long should
       // offers we make be valid by default?
       // A value of "forever" is not allowed.
       // Optional @since **v22** (before the setting was mandatory).
       // If not provided, the previous setting will now simply be preserved.
       default_pay_delay?: RelativeTime;
 
       // If the frontend does NOT specify a refund deadline, how long should
       // refunds be allowed by default? Added on top of the payment deadline.
       // A value of "forever" is not allowed.
       // @since **v22**
       default_refund_delay?: RelativeTime;
 
       // If the frontend does NOT specify an execution date, how long should
       // we tell the exchange to wait to aggregate transactions before
       // executing the wire transfer?  This delay is added on top of
       // the refund deadline and afterwards subject to rounding
       // via the ``default_wire_transfer_rounding_interval``.
       // A value of "forever" is not allowed.
       // Optional @since **v22** (before the setting was mandatory).
       // If not provided, the previous setting will now simply be preserved.
       default_wire_transfer_delay?: RelativeTime;
 
       // How far should the wire deadline (if computed with the help of
       // the ``default_wire_transfer_delay``) be rounded up to compute
       // the ultimate wire deadline?
       // @since **v22**, defaults to no rounding if not given.
       default_wire_transfer_rounding_interval?: RoundingInterval;
     }
 
 
 Inspecting instances
 ^^^^^^^^^^^^^^^^^^^^
 
 .. _instances:
 .. http:get:: /management/instances
 
   This is used to return the list of all the merchant instances.
   It is only available for the implicit ``admin`` instance.
 
   **Required permission:** ``instances-read``
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The backend has successfully returned the list of instances stored. Returns
     a `InstancesResponse`.
 
   **Details:**
 
   .. ts:def:: InstancesResponse
 
     interface InstancesResponse {
       // List of instances that are present in the backend (see `Instance`).
       instances: Instance[];
     }
 
   The `Instance` object describes the instance registered with the backend.
   It does not include the full details, only those that usually concern the frontend.
   It has the following structure:
 
   .. ts:def:: Instance
 
     interface Instance {
       // Merchant name corresponding to this instance.
       name: string;
 
       // Merchant public website.
       website?: string;
 
       // Merchant logo.
       logo?: ImageDataUrl;
 
       // Merchant instance this response is about ($INSTANCE).
       id: string;
 
       // Public key of the merchant/instance, in Crockford Base32 encoding.
       merchant_pub: EddsaPublicKey;
 
       // List of the payment targets supported by this instance. Clients can
       // specify the desired payment target in /order requests.  Note that
       // front-ends do not have to support wallets selecting payment targets.
       payment_targets: string[];
 
       // Has this instance been deleted (but not purged)?
       deleted: boolean;
    }
 
 
 .. http:get:: /management/instances/$INSTANCE
 .. http:get:: [/instances/$INSTANCE]/private
 
   This is used to query a specific merchant instance.  GET operations against
   an instance are authenticated by checking that an authorization is provided
   that matches either the credential required by the instance being modified
   OR the ``admin`` instance, depending on the access path used.
 
   This endpoint may be used even when mandatory TAN channels
   were not validated yet.
 
   **Required permission:** ``instances-read``
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The backend has successfully returned the list of instances stored. Returns
     a `QueryInstancesResponse`.
 
   **Details:**
 
   .. ts:def:: QueryInstancesResponse
 
     interface QueryInstancesResponse {
 
       // Merchant name corresponding to this instance.
       name: string;
 
       // Merchant email for customer contact and password reset.
       email?: string;
 
       // True if the ``email`` address was validated.
       // @since **v21**.
       email_validated?: boolean;
 
       // Merchant phone number for password reset (2-FA)
       // @since **v21**.
       phone_number?: string;
 
       // True if the ``email`` address was validated.
       // @since **v21**.
       phone_validated?: boolean;
 
       // Merchant public website.
       website?: string;
 
       // Merchant logo.
       logo?: ImageDataUrl;
 
       // Public key of the merchant/instance, in Crockford Base32 encoding.
       merchant_pub: EddsaPublicKey;
 
       // The merchant's physical address (to be put into contracts).
       address: Location;
 
       // The jurisdiction under which the merchant conducts its business
       // (to be put into contracts).
       jurisdiction: Location;
 
       // Use STEFAN curves to determine default fees?
       // If false, no fees are allowed by default.
       // Can always be overridden by the frontend on a per-order basis.
       use_stefan: boolean;
 
       // If the frontend does NOT specify a payment deadline, how long should
       // offers we make be valid by default? Added to the order creation
       // time.
       default_pay_delay: RelativeTime;
 
       // If the frontend does NOT specify a refund deadline, how long should
       // refunds be allowed by default? Added to the payment deadline.
       // @since **v22**
       default_refund_delay: RelativeTime;
 
       // If the frontend does NOT specify an execution date, how long should
       // we tell the exchange to wait to aggregate transactions before
       // executing the wire transfer?  This delay is added to the
       // refund deadline and subject to rounding to the
       // ``default_wire_transfer_rounding_interval``.
       default_wire_transfer_delay: RelativeTime;
 
       // Default interval to which wire deadlines computed by
       // adding the wire_transfer_delay on top of the refund
       // deadline should be rounded up to.
       // @since **v23**
       default_wire_transfer_rounding_interval: RoundingInterval;
 
       // Authentication configuration.
       // Does not contain the token when token auth is configured.
       auth: {
         method: "external" | "token";
       };
 
     }
 
 
 Getting statistics
 ^^^^^^^^^^^^^^^^^^
 
 .. http:get:: /management/instances/$INSTANCE/statistics-amount/$SLUG
 .. http:get:: [/instances/$INSTANCE]/private/statistics-amount/$SLUG
 
   This request will return be used to statistics where the
   values are amounts.  All available values for the given
   SLUG will be returned.
   Since protocol **vSTATISTICS**.
 
   **Required permission:** ``statistics-read``
 
   **Request:**
 
   :query by: *Optional*. If set to "BUCKET", only statistics by bucket will be returned. If set to "INTERVAL", only statistics kept by interval will be returned. If not set or set to "ANY", both will be returned.
 
   **Response:**
 
   :http:statuscode:`200 Ok`:
     The body will be a `MerchantStatisticsAmountResponse`
   :http:statuscode:`401 Unauthorized`:
     The request is unauthorized.
   :http:statuscode:`404 Not found`:
     The instance is unknown to the backend.
 
   **Details:**
 
   .. ts:def:: MerchantStatisticsAmountResponse
 
     interface MerchantStatisticsAmountResponse {
 
       // Statistics kept for a particular fixed time window.
       buckets: MerchantStatisticAmountByBucket[];
 
       // Human-readable bucket statistic description.
       // Unset if no buckets returned
       buckets_description?: string;
 
       // Statistics kept for a particular sliding interval.
       intervals: MerchantStatisticAmountByInterval[];
 
       // Human-readable interval statistic description.
       // Unset if no buckets returned
       intervals_description?: string;
     }
 
   .. ts:def:: MerchantStatisticAmountByBucket
 
     interface MerchantStatisticAmountByBucket {
 
        // Start time of the bucket (inclusive)
        start_time: Timestamp;
 
        // End time of the bucket (exclusive)
        end_time: Timestamp;
 
        // Range of the bucket
        range: StatisticBucketRange;
 
        // Sum of all amounts falling under the given
        // SLUG within this timeframe.
        cumulative_amounts: Amount[];
 
     }
 
   .. ts:def:: MerchantStatisticAmountByInterval
 
     interface MerchantStatisticAmountByInterval {
 
        // Start time of the interval.
        // The interval always ends at the response
        // generation time.
        start_time: Timestamp;
 
        // Sum of all amounts falling under the given
        // SLUG within this timeframe.
        cumulative_amounts: Amount[];
 
     }
 
 .. http:get:: /management/instances/$INSTANCE/statistics-counter/$SLUG
 .. http:get:: [/instances/$INSTANCE]/private/statistics-counter/$SLUG
 
   This request will return be used to statistics where the
   values are counters.  All available values for the given
   SLUG will be returned.
   Since protocol **vSTATISTICS**.
 
   **Required permission:** ``statistics-read``
 
   **Request:**
 
     :query by: *Optional*. If set to "BUCKET", only statistics by bucket will be returned. If set to "INTERVAL", only statistics kept by interval will be returned. If not set or set to "ANY", both will be returned.
 
   **Response:**
 
   :http:statuscode:`200 Ok`:
     The body will be a `MerchantStatisticsCounterResponse`
   :http:statuscode:`401 Unauthorized`:
     The request is unauthorized.
   :http:statuscode:`404 Not found`:
     The instance is unknown to the backend.
 
   **Details:**
 
   .. ts:def:: MerchantStatisticsCounterResponse
 
     interface MerchantStatisticsCounterResponse {
 
       // Statistics kept for a particular fixed time window.
       buckets: MerchantStatisticCounterByBucket[];
 
       // Human-readable bucket statistic description.
       // Unset if no buckets returned
       buckets_description?: string;
 
       // Statistics kept for a particular sliding interval.
       intervals: MerchantStatisticCounterByInterval[];
 
       // Human-readable interval statistic description.
       // Unset if no intervals returned
       intervals_description?: string;
 
     }
 
   .. ts:def:: MerchantStatisticCounterByBucket
 
     interface MerchantStatisticCounterByBucket {
 
       // Start time of the bucket (inclusive)
       start_time: Timestamp;
 
       // End time of the bucket (exclusive)
       end_time: Timestamp;
 
       // Range of the bucket
       range: StatisticBucketRange;
 
       // Sum of all counters falling under the given
       // SLUG within this timeframe.
       cumulative_counter: Integer;
 
     }
 
   .. ts:def:: MerchantStatisticCounterByInterval
 
     interface MerchantStatisticCounterByInterval {
 
       // Start time of the interval.
       // The interval always ends at the response
       // generation time.
       start_time: Timestamp;
 
       // Sum of all counters falling under the given
       // SLUG within this timeframe.
       cumulative_counter: Integer;
 
     }
 
 Deleting instances
 ^^^^^^^^^^^^^^^^^^
 
 .. http:delete:: /management/instances/$INSTANCE
 .. http:delete:: [/instances/$INSTANCE]/private
 
   This request will be used to delete (permanently disable)
   or purge merchant instance in the backend. Purging will
   delete all offers and payments associated with the instance,
   while disabling (the default behavior) only deletes the private key
   and makes the instance unusable for new orders or payments.
 
   For deletion, the authentication credentials must match
   the instance that is being deleted or the ``admin``
   instance, depending on the access path used.
 
   **Required permission:** ``instances-write``
 
   **Request:**
 
   :query purge: *Optional*. If set to YES, the instance will be fully
       deleted. Otherwise only the private key would be deleted.
 
   **Response:**
 
   :http:statuscode:`202 Accepted`:
     2FA is required for this operation, usually to validate the
     email and/or phone numbers registered for the instance.
     This returns the `ChallengeResponse`. @since **v21**
   :http:statuscode:`204 No content`:
     The backend has successfully removed the instance.  The body is empty.
   :http:statuscode:`401 Unauthorized`:
     The request is unauthorized. Note that for already deleted instances,
     the request must be authorized using the ``admin`` instance.
   :http:statuscode:`404 Not found`:
     The instance is unknown to the backend.
   :http:statuscode:`409 Conflict`:
     The instance cannot be deleted because it has pending offers, or
     the instance cannot be purged because it has successfully processed
     payments that have not passed the ``TAX_RECORD_EXPIRATION`` time.
     The latter case only applies if ``purge`` was set.
 
 
 KYC status checks
 ^^^^^^^^^^^^^^^^^
 
 .. _merchantkycstatus:
 
 .. http:GET:: /management/instances/$INSTANCE/kyc
 .. http:GET:: /instances/$INSTANCE/private/kyc
 
   Check KYC status of a particular payment target.
   Prompts the exchange to inquire with the bank
   as to the KYC status of the respective account
   and returns the result.
 
   **Required permission:** ``instances-kyc-read``
 
   **Request:**
 
   :query h_wire=H_WIRE: *Optional*. If specified, the KYC check should return the KYC status only for this wire account. Otherwise, for all wire accounts.
   :query exchange_url=URL: *Optional*. If specified, the KYC check should return the KYC status only for the given exchange. Otherwise, for all exchanges we interacted with.
   :query lpt=TARGET: *Optional*.
     Specifies what status change we are long-polling for.
     Use 1 to wait for the KYC auth transfer (access token available),
     2 to wait for an AML investigation to be done,
     and 3 to wait for the KYC status to be OK.
     If multiple accounts or exchanges match the query,
     any account reaching the TARGET state will cause
     the response to be returned.
     Since protocol **v17**.
   :query timeout_ms=NUMBER: *Optional.*  If specified, the merchant will
     wait up to ``timeout_ms`` milliseconds for the exchanges to confirm completion of the KYC process(es).
 
   **Response:**
 
   If different exchanges cause different errors when processing
   the request, the largest HTTP status code that is applicable
   is returned.
 
   :http:statuscode:`200 Ok`:
     The user may be redirected to the provided locations to perform
     KYC checks.
     The response will be a `MerchantAccountKycRedirectsResponse` object.
     Uses this status code and format only since protocol **v17**.
   :http:statuscode:`204 No content`:
     No possibilities for KYC operations exist.
     This may change in the future, but there is
     no need to check again soon. This will most likely
     change if accounts are added to the instance.
 
   **Details:**
 
   .. ts:def:: MerchantAccountKycRedirectsResponse
 
      interface MerchantAccountKycRedirectsResponse {
 
        // Array of KYC status information for
        // the exchanges and bank accounts selected
        // by the query.
        kyc_data: MerchantAccountKycRedirect[];
 
     }
 
   .. ts:def:: MerchantAccountKycRedirect
 
     interface MerchantAccountKycRedirect {
 
       // Summary of the status of the KYC process. Possible values are:
       //
       // o "no-exchange-keys": we do not (yet) have the /keys of the exchange
       // - "kyc-wire-impossible": KYC auth transfer needed but not possible
       // @ "kyc-wire-required": KYC auth transfer still needed and possible
       // @ "kyc-required": merchant must supply KYC data to proceed (incl.
       //      in case of exposed zero-limits on deposit/aggregation)
       // + "awaiting-aml-review": account under review by payment provider
       // + "ready": everything is fine, account can be fully used
       // - "logic-bug": merchant backend logic bug
       // o "merchant-internal-error": merchant had an internal error
       // o "exchange-internal-error": exchange had an internal error
       // o "exchange-gateway-timeout": network timeout at gateway
       // o "exchange-unreachable": exchange did not respond at all
       // - "exchange-status-invalid": exchange violated protocol in reply
       //
       // "+" are perfectly normal states, "@" are states where the user
       // must performn an action (show link!); "o" are reasonable transient
       // states that could happen and are we are expected to likely recover
       // from automatically but that we should inform the user about
       // (show in yellow?), "-" are hard error states from which
       // there is likely no good automatic recovery from (show in red?).
       status: string;
 
       // Full payto URI of the bank wire account this is about.
       payto_uri: string;
 
       // Hash of the salted payto://-URI of our
       // bank wire account this is about.
       // Since protocol **v17**.
       h_wire: string;
 
       // Base URL of the exchange this is about.
       exchange_url: string;
 
       // HTTP status code returned by the exchange when we asked for
       // information about the KYC status.
       // Since protocol **v17**.
       exchange_http_status: Integer;
 
       // True if we did not get a ``/keys`` response from
       // the exchange and thus cannot do certain checks, such as
       // determining default account limits or account eligibility.
       no_keys: boolean;
 
       // True if the given account cannot to KYC at the
       // given exchange because no wire method exists that could
       // be used to do the KYC auth wire transfer.
       auth_conflict: boolean;
 
       // Numeric `error code <error-codes>` indicating errors the exchange
       // returned, or TALER_EC_INVALID for none.
       // Optional (as there may not always have
       // been an error code). Since protocol **v17**.
       exchange_code?: Integer;
 
       // Access token needed to open the KYC SPA and/or
       // access the ``/kyc-info/`` endpoint.
       access_token?: AccountAccessToken;
 
       // Array with limitations that currently apply to this
       // account and that may be increased or lifted if the
       // KYC check is passed.
       // Note that additional limits *may* exist and not be
       // communicated to the client. If such limits are
       // reached, this *may* be indicated by the account
       // going into ``aml_review`` state. However, it is
       // also possible that the exchange may legally have
       // to deny operations without being allowed to provide
       // any justification.
       // The limits should be used by the client to
       // possibly structure their operations (e.g. withdraw
       // what is possible below the limit, ask the user to
       // pass KYC checks or withdraw the rest after the time
       // limit is passed, warn the user to not withdraw too
       // much or even prevent the user from generating a
       // request that would cause it to exceed hard limits).
       limits?: AccountLimit[];
 
       // Array of full payto://-URIs with
       // wire transfer instructions (including
       // optional amount and subject) for a KYC auth wire
       // transfer. Set only if this is required
       // to get the given exchange working.
       // Array because the exchange may have multiple
       // bank accounts, in which case any of these
       // accounts will do.
       // Optional. Since protocol **v17**.
       payto_kycauths?: string[];
 
     }
 
 
 -------------
 Bank Accounts
 -------------
 
 One or more bank accounts must be associated with an instance
 so that the instance can receive payments.  Payments may be made
 into any of the active bank accounts of an instance.
 
 
 .. http:post:: [/instances/$INSTANCE]/private/accounts
 
   This is used to add an account to an instance.
 
   **Required permission:** ``accounts-write``
 
   **Request:**
 
   The request must have an `AccountAddDetails` body.
 
   **Response:**
 
   :http:statuscode:`200 Ok`:
     Adding the account was successful, we return the salt selected by the backend and the resulting wire hash in an `AccountAddResponse`.
   :http:statuscode:`202 Accepted`:
     2FA is required for this operation, usually to validate the
     email and/or phone numbers registered for the instance.
     This returns the `ChallengeResponse`. @since **v21**
   :http:statuscode:`404 Not found`:
     The merchant instance is unknown or it is not in our data.
   :http:statuscode:`409 Conflict`:
     The provided information is inconsistent with the current state of the instance.
     Usually this means we already have this account, but with conflicting credit facade information.
     Inactive accounts can be reactivated using this method even if the
     credit facade information differs from the previous state.
 
   **Details:**
 
   .. ts:def:: AccountAddDetails
 
     interface AccountAddDetails {
 
       // Full payto:// URI of the account.
       payto_uri: string;
 
       // URL from where the merchant can download information
       // about incoming wire transfers to this account.
       credit_facade_url?: string;
 
       // Credentials to use when accessing the credit facade.
       // Never returned on a GET (as this may be somewhat
       // sensitive data). Can be set in POST
       // or PATCH requests to update (or delete) credentials.
       // To really delete credentials, set them to the type: "none".
       credit_facade_credentials?: FacadeCredentials;
 
     }
 
   .. ts:def:: FacadeCredentials
 
     type FacadeCredentials =
       | NoFacadeCredentials
       | BasicAuthFacadeCredentials;
 
   .. ts:def:: NoFacadeCredentials
 
     interface NoFacadeCredentials {
        type: "none";
     };
 
   .. ts:def:: BasicAuthFacadeCredentials
 
     interface BasicAuthFacadeCredentials {
        type: "basic";
 
        // Username to use to authenticate
        username: string;
 
        // Password to use to authenticate
        password: string;
     };
 
   .. ts:def:: AccountAddResponse
 
     interface AccountAddResponse {
 
       // Hash over the wire details (including over the salt).
       h_wire: HashCode;
 
       // Salt used to compute h_wire.
       salt: HashCode;
 
     }
 
 
 .. http:patch:: [/instances/$INSTANCE]/private/accounts/$H_WIRE
 
   This is used to update a bank account.
 
   **Required permission:** ``accounts-write``
 
   **Request:**
 
   The request must be a `AccountPatchDetails`.
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The account has successfully modified.
   :http:statuscode:`404 Not found`:
     The account (``H_WIRE``) is unknown to the backend.
 
   **Details:**
 
   .. ts:def:: AccountPatchDetails
 
    interface AccountPatchDetails {
 
       // URL from where the merchant can download information
       // about incoming wire transfers to this account.
       credit_facade_url?: string;
 
       // Credentials to use when accessing the credit facade.
       // Never returned on a GET (as this may be somewhat
       // sensitive data). Can be set in POST
       // or PATCH requests to update (or delete) credentials.
       // To really delete credentials, set them to the type: "none".
       // If the argument is omitted, the old credentials
       // are simply preserved.
       credit_facade_credentials?: FacadeCredentials;
    }
 
 
 .. http:get:: [/instances/$INSTANCE]/private/accounts
 
   This is used to return the list of all the bank accounts
   of an instance.
 
   **Required permission:** ``accounts-read``
 
   **Response:**
 
   :http:statuscode:`200 OK`:
      The backend has successfully returned all the accounts. Returns a `AccountsSummaryResponse`.
   :http:statuscode:`404 Not found`:
      The backend has does not know about the instance.
 
   **Details:**
 
   .. ts:def:: AccountsSummaryResponse
 
     interface AccountsSummaryResponse {
 
       // List of accounts that are known for the instance.
       accounts: BankAccountEntry[];
     }
 
   .. ts:def:: BankAccountEntry
 
     interface BankAccountEntry {
 
       // Full payto:// URI of the account.
       payto_uri: string;
 
       // Hash over the wire details (including over the salt).
       h_wire: HashCode;
 
       // true if this account is active,
       // false if it is historic.
       active: boolean;
     }
 
 .. http:get:: [/instances/$INSTANCE]/private/accounts/$H_WIRE
 
   This is used to obtain detailed information about a specific bank account.
 
 
   **Required permission:** ``accounts-read``
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The backend has successfully returned the detailed information about a specific bank account.
     Returns a `BankAccountDetail`.
   :http:statuscode:`404 Not found`:
     The bank account or instance is unknown to the backend.
 
   **Details:**
 
   .. ts:def:: BankAccountDetail
 
     interface BankAccountDetail {
 
       // Full payto:// URI of the account.
       payto_uri: string;
 
       // Hash over the wire details (including over the salt).
       h_wire: HashCode;
 
       // Salt used to compute h_wire.
       salt: HashCode;
 
       // URL from where the merchant can download information
       // about incoming wire transfers to this account.
       credit_facade_url?: string;
 
       // true if this account is active,
       // false if it is historic.
       active: boolean;
     }
 
 
 
 .. http:delete:: [/instances/$INSTANCE]/private/accounts/$H_WIRE
 
   **Required permission:** ``accounts-write``
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The backend has successfully deactivated the account.
   :http:statuscode:`404 Not found`:
     The backend does not know the instance or the account.
 
 
 --------------------
 Inventory management
 --------------------
 
 .. _inventory:
 
 Inventory management is an *optional* backend feature that can be used to
 manage limited stocks of products and to auto-complete product descriptions in
 contracts (such that the frontends have to do less work).  You can use the
 Taler merchant backend to process payments *without* using its inventory
 management.
 
 
 Managing measurement units
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 .. http:get:: [/instances/$INSTANCE]/private/units
 
   Returns the list of measurement units available to an instance.
 
   **Required permission:** ``units-read``
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The backend returned the unit catalog. The body is a `UnitListResponse`.
 
   **Details:**
 
   .. ts:def:: UnitListResponse
 
     interface UnitListResponse {
       units: MerchantUnit[];
     }
 
   .. ts:def:: MerchantUnit
 
     interface MerchantUnit {
       // Unique serial for the unit.
       unit_serial: Integer;
 
       // Short identifier used in product definitions.
       unit: string;
 
       // Human-readable long label.
       unit_name_long: string;
 
       // Human-readable short label.
       unit_name_short: string;
 
       // Optional translations for the long label.
       unit_name_long_i18n?: { [lang_tag: string]: string };
 
       // Optional translations for the short label.
       unit_name_short_i18n?: { [lang_tag: string]: string };
 
       // Whether fractional quantities are allowed for this unit.
       unit_allow_fraction: boolean;
 
       // Maximum fractional precision (0-6) enforced for this unit.
       unit_precision_level: Integer;
 
       // Whether the unit is currently active.
       unit_active: boolean;
 
       // True if the unit is provided by the backend and cannot be removed.
       unit_builtin: boolean;
     }
 
 .. http:get:: [/instances/$INSTANCE]/private/units/$UNIT
 
   Fetch details for a single measurement unit.
 
   **Required permission:** ``units-read``
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The backend returned the unit definition. The body is a `MerchantUnit`.
   :http:statuscode:`404 Not found`:
     The unit is unknown to the backend.
 
 .. http:post:: [/instances/$INSTANCE]/private/units
 
   Create a custom measurement unit or reactivate a previously disabled one.
 
   **Required permission:** ``units-write``
 
   **Request:**
 
   The request must be a `UnitAddRequest`.
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The backend added the unit.
   :http:statuscode:`409 Conflict`:
     A built-in unit with the same short name already exists.
 
   .. ts:def:: UnitAddRequest
 
     interface UnitAddRequest {
       // Short identifier to reference the unit from products and orders.
       unit: string;
 
       // Human-readable long label (e.g. "kilogram").
       unit_name_long: string;
 
       // Human-readable short label (e.g. "kg").
       unit_name_short: string;
 
       // Optional translations for the long label keyed by BCP 47 language tags.
       unit_name_long_i18n?: { [lang_tag: string]: string };
 
       // Optional translations for the short label keyed by BCP 47 language tags.
       unit_name_short_i18n?: { [lang_tag: string]: string };
 
       // Defaults to false; set to true to enable fractional quantities.
       unit_allow_fraction?: boolean;
 
       // Fractional precision (0-6). Ignored when ``unit_allow_fraction`` is false.
       unit_precision_level?: Integer;
 
       // Defaults to true.
       unit_active?: boolean;
     }
 
 .. http:patch:: [/instances/$INSTANCE]/private/units/$UNIT
 
   Update attributes of a measurement unit.
 
   **Required permission:** ``units-write``
 
   **Request:**
 
   The request must be a `UnitPatchRequest`.
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The backend updated the unit.
   :http:statuscode:`404 Not found`:
     The unit is unknown to the backend.
 
   Built-in units allow changing ``unit_allow_fraction``, ``unit_precision_level``, and
   ``unit_active``; other fields are immutable for built-ins.
 
   .. ts:def:: UnitPatchRequest
 
     interface UnitPatchRequest {
       // Updated human-readable long label.
       unit_name_long?: string;
 
       // Updated human-readable short label.
       unit_name_short?: string;
 
       // Updated translations for the long label keyed by BCP 47 language tags.
       unit_name_long_i18n?: { [lang_tag: string]: string };
 
       // Updated translations for the short label keyed by BCP 47 language tags.
       unit_name_short_i18n?: { [lang_tag: string]: string };
 
       // Override to allow or forbid fractional quantities.
       unit_allow_fraction?: boolean;
 
       // Override for the fractional precision (0-6). Ignored if fractions are disabled.
       unit_precision_level?: Integer;
 
       // Toggle whether the unit is active.
       unit_active?: boolean;
     }
 
   Fractional precision is capped at six decimal places. Disabling
   ``unit_allow_fraction`` forces ``unit_precision_level`` to zero.
 
 .. http:delete:: [/instances/$INSTANCE]/private/units/$UNIT
 
   Remove a custom unit from an instance.
 
     **Required permission:** ``units-write``
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The unit was removed.
   :http:statuscode:`404 Not found`:
     The unit is unknown to the backend.
   :http:statuscode:`409 Conflict`:
     Built-in units cannot be deleted.
 
 
 Managing product categories
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 .. http:get:: [/instances/$INSTANCE]/private/categories
 
   This request returns the known product categories
   and the number of products in each category.
   Since API version **v16**.
 
   **Required permission:** ``categories-read``
 
   **Response:**
 
   :http:statuscode:`200 Ok`:
     The body is a `CategoryListResponse`.
 
   **Details:**
 
   .. ts:def:: CategoryListResponse
 
     interface CategoryListResponse {
 
       // Array with all of the categories we know.
       categories: CategoryListEntry[];
 
     }
 
   .. ts:def:: CategoryListEntry
 
     interface CategoryListEntry {
 
       // Unique number for the category.
       category_id: Integer;
 
       // Name of the category.
       name: string;
 
       // Translations of the name into various
       // languages.
       name_i18n?: { [lang_tag: string]: string };
 
       // Number of products in this category.
       // A product can be in more than one category.
       product_count: Integer;
 
     }
 
 .. http:get:: [/instances/$INSTANCE]/private/categories/$CATEGORY_ID
 
   This request returns the known products in the given
   category.
   Since API version **v16**.
 
   **Required permission:** ``categories-read``
 
   **Response:**
 
   :http:statuscode:`200 Ok`:
     The body is a `CategoryProductList`.
 
   **Details:**
 
   .. ts:def:: CategoryProductList
 
     interface CategoryProductList {
 
       // Name of the category.
       name: string;
 
       // Translations of the name into various
       // languages.
       name_i18n?: { [lang_tag: string]: string };
 
       // The products in this category.
       products: CategoryProductSummary[];
 
     }
 
   .. ts:def:: CategoryProductSummary
 
     interface CategoryProductSummary {
 
       // ID of a product in the category.
       product_id: string;
 
     }
 
 
 .. http:post:: [/instances/$INSTANCE]/private/categories
 
   This is used to create a new category for the inventory.
   Since API version **v16**.
 
   **Required permission:** ``categories-write``
 
   **Request:**
 
     The request is a `CategoryCreateRequest`.
 
   **Response:**
 
   :http:statuscode:`200 Ok`:
     The response is a `CategoryCreatedResponse`.
 
   **Details:**
 
   .. ts:def:: CategoryCreateRequest
 
     interface CategoryCreateRequest {
 
       // Name of the category.
       name: string;
 
       // Translations of the name into various
       // languages.
       name_i18n?: { [lang_tag: string]: string };
 
     }
 
   .. ts:def:: CategoryCreatedResponse
 
     interface CategoryCreatedResponse {
 
       // Number of the newly created category.
       category_id: Integer;
     }
 
 
 .. http:patch:: [/instances/$INSTANCE]/private/categories/$CATEGORY_ID
 
   This is used to edit a category.
   Since API version **v16**.
 
   **Required permission:** ``categories-write``
 
   **Request:**
 
     The request is a `CategoryCreateRequest`.
 
   **Response:**
 
   :http:statuscode:`204 No Content`:
     The category was modified successfully.
 
 .. http:delete:: [/instances/$INSTANCE]/private/categories/$CATEGORY_ID
 
   This is used to delete a category.
   Since API version **v16**.
 
   **Required permission:** ``categories-write``
 
   **Response:**
 
   :http:statuscode:`204 No Content`:
     The category was deleted.
   :http:statuscode:`404 Not Found`:
     The category was possibly already deleted or is unknown.
 
 
 Adding products to the inventory
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 
 .. http:post:: [/instances/$INSTANCE]/private/products
 
   This is used to add a product to the inventory.
 
   **Required permission:** ``products-write``
 
   **Request:**
 
   The request must be a `ProductAddDetail`.
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The backend has successfully expanded the inventory.
   :http:statuscode:`409 Conflict`:
     The backend already knows a product with this product ID, but with different details.
 
   **Details:**
 
   .. ts:def:: ProductAddDetail
 
     interface ProductAddDetail {
 
       // Product ID to use.
       product_id: string;
 
       // Human-readable product name.
       // Since API version **v20**.  Optional only for
       // backwards-compatibility, should be considered mandatory
       // moving forward!
       product_name?: string;
 
       // Human-readable product description.
       description: string;
 
       // Map from IETF BCP 47 language tags to localized descriptions.
       description_i18n?: { [lang_tag: string]: string };
 
       // Categories into which the product belongs.
       // Used in the POS-endpoint.
       // Since API version **v16**.
       categories?: Integer[];
 
       // Unit in which the product is measured (liters, kilograms, packages, etc.).
       unit: string;
 
       // Optional override to control whether fractional quantities are permitted.
       // Defaults to the policy implied by ``unit``.
       unit_allow_fraction?: boolean;
 
       // Override for the fractional precision level (0-6). Only relevant if
       // ``unit_allow_fraction`` is true. Defaults come from ``unit``.
       unit_precision_level?: Integer;
 
       // Preferred way to express inventory counts using "<integer>[.<fraction>]" syntax.
       // Use "-1" for unlimited stock. Required unless ``total_stock`` is provided.
       unit_total_stock?: string;
 
       // Legacy stock counter. Deprecated, use ``unit_total_stock`` instead.
       // Still required when ``unit_total_stock`` is omitted.
       total_stock?: Integer;
 
       // Preferred way to express the per-unit price of the product. Supply at least one entry;
       // the first entry represents the base price and MUST include applicable taxes.
       // Zero implies that the product is not sold separately or that the price must be supplied
       // by the frontend.
       unit_price?: Amount[];
 
       // Legacy price field. Deprecated; when present it must match the first element of ``unit_price``.
       price?: Amount;
 
       // An optional base64-encoded product image.
       image?: ImageDataUrl;
 
       // A list of taxes paid by the merchant for one unit of this product.
       taxes?: Tax[];
 
       // Identifies where the product is in stock.
       address?: Location;
 
       // Identifies when we expect the next restocking to happen.
       next_restock?: Timestamp;
 
       // Minimum age buyer must have (in years). Default is 0.
       minimum_age?: Integer;
 
     }
 
   Clients SHOULD migrate to the new ``unit_*`` fields and treat ``total_stock`` and ``price``
   as deprecated compatibility shims. If both the legacy and the new representation are supplied,
   their values must match. Omitting both ``unit_total_stock`` and ``total_stock`` (or both
   ``unit_price`` and ``price``) results in a ``400 Bad Request``. When only ``price`` is given,
   the backend treats it as a one-element ``unit_price`` array.
 
   ``unit_total_stock`` uses a fixed-point decimal string in the form ``INTEGER[.FRACTION]`` with
   at most six fractional digits. Scientific notation or special values such as ``NaN`` are not
   accepted. Supply ``"-1"`` to represent unlimited stock.
 
   Fractional behaviour defaults to the value of ``unit``. The backend disables fractions for
   ``Piece``, ``Set``, ``Custom``, ``WeightUnitMg`` and ``SizeUnitMm``. Other predefined units
   allow fractional quantities with the following default precision levels:
 
   - Precision ``1``: ``WeightUnitG``, ``SizeUnitCm``, ``SurfaceUnitMm2``, ``VolumeUnitMm3``.
   - Precision ``2``: ``WeightUnitOunce``, ``SizeUnitInch``, ``SurfaceUnitCm2``,
     ``VolumeUnitInch3``, ``VolumeUnitOunce``, ``TimeUnitHour``, ``TimeUnitMonth``.
   - Precision ``3``: ``WeightUnitTon``, ``WeightUnitKg``, ``WeightUnitPound``, ``SizeUnitM``,
     ``SizeUnitDm``, ``SizeUnitFoot``, ``SurfaceUnitDm2``, ``SurfaceUnitFoot2``, ``VolumeUnitCm3``,
     ``VolumeUnitLitre``, ``VolumeUnitGallon``, ``TimeUnitSecond``, ``TimeUnitMinute``,
     ``TimeUnitDay``, ``TimeUnitWeek``.
   - Precision ``4``: ``SurfaceUnitM2``, ``SurfaceUnitInch2``, ``TimeUnitYear``.
   - Precision ``5``: ``VolumeUnitDm3``, ``VolumeUnitFoot3``.
   - Precision ``6``: ``VolumeUnitM3``.
 
   Integrations can override these defaults by explicitly setting ``unit_allow_fraction`` and/or
   ``unit_precision_level``.
 
 
 .. http:patch:: [/instances/$INSTANCE]/private/products/$PRODUCT_ID
 
   This is used to update product details in the inventory. Note that the
   ``total_stock`` and ``total_lost`` numbers MUST be greater or equal than
   previous values (this design ensures idempotency).  In case stocks were lost
   but not sold, increment the ``total_lost`` number.  All fields in the
   request are optional, those that are not given are simply preserved (not
   modified).  Note that the ``description_i18n`` and ``taxes`` can only be
   modified in bulk: if it is given, all translations must be provided, not
   only those that changed.  ``never`` should be used for the ``next_restock``
   timestamp to indicate no intention/possibility of restocking, while a time
   of zero is used to indicate "unknown".
 
   **Required permission:** ``products-write``
 
   **Request:**
 
   The request must be a `ProductPatchDetail`.
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The backend has successfully expanded the inventory.
   :http:statuscode:`404 Not found`:
     The product (ID) is unknown to the backend.
   :http:statuscode:`409 Conflict`:
     The provided information is inconsistent with the current state of the inventory.
 
 
   .. ts:def:: ProductPatchDetail
 
     interface ProductPatchDetail {
 
       // Human-readable product name.
       // Since API version **v20**.  Optional only for
       // backwards-compatibility, should be considered mandatory
       // moving forward!
       product_name?: string;
 
       // Human-readable product description.
       description: string;
 
       // Map from IETF BCP 47 language tags to localized descriptions.
       description_i18n?: { [lang_tag: string]: string };
 
       // Unit in which the product is measured (liters, kilograms, packages, etc.).
       unit: string;
 
       // Optional override to control whether fractional quantities are permitted.
       unit_allow_fraction?: boolean;
 
       // Override for the fractional precision level (0-6). Only relevant if
       // ``unit_allow_fraction`` is true.
       unit_precision_level?: Integer;
 
       // Categories into which the product belongs.
       // Used in the POS-endpoint.
       // Since API version **v16**.
       categories?: Integer[];
 
       // Preferred way to express the per-unit price. Supply at least one entry;
       // the first entry represents the base price and MUST include applicable taxes.
       // Zero implies that the product is not sold separately or that the price must be supplied
       // by the frontend.
       unit_price?: Amount[];
 
       // Legacy price field. Deprecated; when present it must match the first element of ``unit_price``.
       price?: Amount;
 
       // An optional base64-encoded product image.
       image?: ImageDataUrl;
 
       // A list of taxes paid by the merchant for one unit of this product.
       taxes?: Tax[];
 
       // Preferred way to express inventory counts using "<integer>[.<fraction>]" syntax.
       // Use "-1" for unlimited stock.
       unit_total_stock?: string;
 
       // Legacy stock counter. Deprecated, use ``unit_total_stock`` instead.
       total_stock?: Integer;
 
       // Number of units of the product that were lost (spoiled, stolen, etc.).
       total_lost?: Integer;
 
       // Identifies where the product is in stock.
       address?: Location;
 
       // Identifies when we expect the next restocking to happen.
       next_restock?: Timestamp;
 
       // Minimum age buyer must have (in years). Default is 0.
       minimum_age?: Integer;
 
     }
 
   The same compatibility rules for the ``unit_*`` fields and their deprecated counterparts apply
   when patching an existing product.
 
 Inspecting inventory
 ^^^^^^^^^^^^^^^^^^^^
 
 .. http:get:: [/instances/$INSTANCE]/private/products
 
   This is used to return the list of all items in the inventory.
 
   **Required permission:** ``products-read``
 
   **Request:**
 
   :query limit: *Optional*. At most return the given number of results. Negative for descending by row ID, positive for ascending by row ID. Default is ``20``.  Since protocol **v12**.
   :query offset: *Optional*. Starting ``product_serial_id`` for an iteration.  Since protocol **v12**.
   :query category_filter: *Optional*. Only returns products that are in a category where the category name contains the given text as a substring. Matching is case-insensitive. Since protocol **v23**.
   :query name_filter: *Optional*. Only returns products where the product name contains the given text as a substring. Matching is case-insensitive. Since protocol **v23**.
   :query description_filter: *Optional*. Only returns products where the product description contains the given text as a substring. Matching is case-insensitive. Since protocol **v23**.
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The backend has successfully returned the inventory. Returns
     a `InventorySummaryResponse`.
   :http:statuscode:`404 Not found`:
     The backend has does not know about the instance.
 
   **Details:**
 
   .. ts:def:: InventorySummaryResponse
 
     interface InventorySummaryResponse {
       // List of products that are present in the inventory.
       products: InventoryEntry[];
     }
 
   The `InventoryEntry` object describes an item in the inventory. It has the following structure:
 
   .. ts:def:: InventoryEntry
 
     interface InventoryEntry {
       // Product identifier, as found in the product.
       product_id: string;
 
       // ``product_serial_id`` of the product in the database.
       product_serial: Integer;
 
     }
 
 
 .. http:get:: [/instances/$INSTANCE]/private/products/$PRODUCT_ID
 
   This is used to obtain detailed information about a product in the inventory.
 
   **Required permission:** ``products-read``
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The backend has successfully returned the inventory. Returns
     a `ProductDetail`.
   :http:statuscode:`404 Not found`:
     The product (ID) is unknown to the backend.
 
   **Details:**
 
   .. ts:def:: ProductDetail
 
     interface ProductDetail {
 
       // Human-readable product name.
       // Since API version **v20**.
       product_name: string;
 
       // Human-readable product description.
       description: string;
 
       // Map from IETF BCP 47 language tags to localized descriptions.
       description_i18n: { [lang_tag: string]: string };
 
       // Unit in which the product is measured (liters, kilograms, packages, etc.).
       unit: string;
 
       // Does the backend allow fractional quantities for this unit?
       unit_allow_fraction: boolean;
 
       // Maximum fractional precision (0-6) enforced for inventory operations.
       unit_precision_level: Integer;
 
       // Categories into which the product belongs.
       // Since API version **v16**.
       categories: Integer[];
 
       // Price tiers for this product. The first entry represents the base price and MUST include
       // applicable taxes. Zero implies the product is not sold separately or that the price is not
       // fixed, and must be supplied by the front-end.
       unit_price: Amount[];
 
       // Legacy price field kept for compatibility. Deprecated; equal to the first element of ``unit_price``.
       price: Amount;
 
       // An optional base64-encoded product image.
       image: ImageDataUrl;
 
       // A list of taxes paid by the merchant for one unit of this product.
       // Optional since **v15**.
       taxes?: Tax[];
 
       // Legacy integer stock counter kept for compatibility. ``-1`` indicates unlimited stock.
       total_stock: Integer;
 
       // Stock expressed using "<integer>[.<fraction>]" syntax with up to six fractional digits.
       // Use ``"-1"`` for unlimited stock.
       unit_total_stock: string;
 
       // Number of units of the product that have already been sold.
       total_sold: Integer;
 
       // Number of units of the product that were lost (spoiled, stolen, etc.).
       total_lost: Integer;
 
       // Identifies where the product is in stock.
       // Optional since **v15**.
       address?: Location;
 
       // Identifies when we expect the next restocking to happen.
       next_restock?: Timestamp;
 
       // Minimum age buyer must have (in years).
       minimum_age?: Integer;
 
     }
 
 .. http:get:: [/instances/$INSTANCE]/private/pos
 
   This is used to return the point-of-sale (POS) configuration with full details on all items in the inventory.
 
   Endpoint was introduced in protocol **v15**.
 
   **Required permission:** ``products-read``
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The backend has successfully returned the inventory. Returns
     a `FullInventoryDetailsResponse`.
   :http:statuscode:`404 Not found`:
     The backend has does not know about the instance.
 
   **Details:**
 
   .. ts:def:: FullInventoryDetailsResponse
 
     interface FullInventoryDetailsResponse {
 
       // List of products that are present in the inventory.
       products: MerchantPosProductDetail[];
 
       // List of categories in the inventory.
       categories: MerchantCategory[];
 
     }
 
   .. ts:def:: MerchantPosProductDetail
 
     interface MerchantPosProductDetail {
 
       // A unique numeric ID of the product
       product_serial: Integer;
 
       // A merchant-internal unique identifier for the product.
       product_id: string;
 
       // Human-readable product name.
       // Since API version **v20**.
       product_name: string;
 
       // A list of category IDs this product belongs to.
       // Typically, a product only belongs to one category, but more than one is supported.
       categories: Integer[];
 
       // Human-readable product description.
       description: string;
 
       // Map from IETF BCP 47 language tags to localized descriptions.
       description_i18n: { [lang_tag: string]: string };
 
       // Unit in which the product is measured (liters, kilograms, packages, etc.).
       unit: string;
 
       // Does the backend allow fractional quantities for this unit?
       unit_allow_fraction: boolean;
 
       // Maximum fractional precision (0-6) enforced for inventory operations.
       unit_precision_level: Integer;
 
       // Price tiers for this product. The first entry represents the base price and MUST include
       // applicable taxes. Zero implies the product is not sold separately or that the price is not
       // fixed, and must be supplied by the front-end.
       unit_price: Amount[];
 
       // Legacy price field kept for compatibility. Deprecated; equal to the first element of ``unit_price``.
       price: Amount;
 
       // An optional base64-encoded product image.
       image?: ImageDataUrl;
 
       // A list of taxes paid by the merchant for one unit of this product.
       taxes?: Tax[];
 
       // Legacy integer stock counter kept for compatibility. ``-1`` indicates unlimited stock.
       total_stock?: Integer;
 
       // Stock expressed using "<integer>[.<fraction>]" syntax with up to six fractional digits.
       // Use ``"-1"`` for unlimited stock.
       unit_total_stock: string;
 
       // Minimum age buyer must have (in years).
       minimum_age?: Integer;
 
     }
 
   .. ts:def:: MerchantCategory
 
     interface MerchantCategory {
       // A unique numeric ID of the category
       id: Integer;
 
       // The name of the category. This will be shown to users and used in the order summary.
       name: string;
 
       // Map from IETF BCP 47 language tags to localized names
       name_i18n?: { [lang_tag: string]: string };
     }
 
 
 Fetching product images
 ^^^^^^^^^^^^^^^^^^^^^^^
 
 .. http:get:: /products/$IMAGE_HASH/image
 
   Returns a stored product image by its content hash. The hash is the lowercase
   hexadecimal SHA-256 digest of the base64-encoded image data supplied in
   ``image`` during product creation or update.
 
   **Required permission:** none (public endpoint)
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The body is a `ProductImageResponse`.
   :http:statuscode:`400 Bad Request`:
     The hash is not a valid hex-encoded SHA-256 digest.
   :http:statuscode:`404 Not found`:
     No image is known for the given hash.
 
   .. ts:def:: ProductImageResponse
 
     interface ProductImageResponse {
       // Data URL containing the product image as stored in the backend.
       image: ImageDataUrl;
     }
 
 
 
 Reserving inventory
 ^^^^^^^^^^^^^^^^^^^
 
 .. http:post:: [/instances/$INSTANCE]/private/products/$PRODUCT_ID/lock
 
   This is used to lock a certain quantity of the product for a limited
   duration while the customer assembles a complete order.  Note that
   frontends do not have to "unlock", they may rely on the timeout as
   given in the ``duration`` field.  Re-posting a lock with a different
   ``duration`` or ``quantity`` updates the existing lock for the same UUID
   and does not result in a conflict.
 
   Unlocking by using a ``quantity`` of zero is
   optional but recommended if customers remove products from the
   shopping cart. Note that actually POSTing to ``/orders`` with set
   ``inventory_products`` and using ``lock_uuids`` will **transition** the
   lock to the newly created order (which may have a different ``duration``
   and ``quantity`` than what was requested in the lock operation).
   If an order is for fewer items than originally locked, the difference
   is automatically unlocked.
 
   **Required permission:** ``products-lock``
 
   **Request:**
 
   The request must be a `LockRequest`.
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The backend has successfully locked (or unlocked) the requested ``quantity``.
   :http:statuscode:`404 Not found`:
     The backend has does not know this product.
   :http:statuscode:`410 Gone`:
     The backend does not have enough of product in stock. Returns an `OutOfStockResponse`.
 
   **Details:**
 
   .. ts:def:: LockRequest
 
     interface LockRequest {
 
       // UUID that identifies the frontend performing the lock
       // Must be unique for the lifetime of the lock.
       lock_uuid: string;
 
       // How long does the frontend intend to hold the lock?
       duration: RelativeTime;
 
       // Legacy integer quantity to lock. Deprecated; defaults to 1 if both
       // ``quantity`` and ``unit_quantity`` are absent.
       quantity?: Integer;
 
       // Preferred way to express the requested quantity using "<integer>[.<fraction>]" syntax.
       unit_quantity?: string;
 
     }
 
   At least one of ``quantity`` or ``unit_quantity`` must be supplied; omitting both defaults to a
   quantity of one. ``unit_quantity`` follows the same decimal-string format described for
   ``unit_total_stock``.
 
   .. note::
 
     The ``GNUNET_CRYPTO_random_timeflake()`` C API can be used
     to generate such timeflakes for clients written in C.
 
 
 Removing products from inventory
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 .. http:delete:: [/instances/$INSTANCE]/private/products/$PRODUCT_ID
 
   Delete information about a product.  Fails if the product is locked by
   anyone.
 
   **Required permission:** ``products-write``
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The backend has successfully deleted the product.
   :http:statuscode:`404 Not found`:
     The backend does not know the instance or the product.
   :http:statuscode:`409 Conflict`:
     The backend refuses to delete the product because it is locked.
 
 
 ------------------
 Payment processing
 ------------------
 
 To process Taler payments, a merchant must first set up an order with
 the merchant backend. The order is then claimed by a wallet, and
 paid by the wallet. The merchant can check the payment status of the
 order. Once the order is paid, the merchant may (for a limited time)
 grant refunds on the order.
 
 Creating orders
 ^^^^^^^^^^^^^^^
 
 .. _post-order:
 
 .. http:post:: [/instances/$INSTANCE]/private/orders
 
   Create a new order that a customer can pay for.
 
   This request is **not** idempotent unless an ``order_id`` is explicitly specified.
   However, while repeating without an ``order_id`` will create another order, that is
   generally pretty harmless (as long as only one of the orders is returned to the wallet).
 
   .. note::
 
     This endpoint does not return a URL to redirect your user to confirm the
     payment.  To get this URL use either
     :http:get:`[/instances/$INSTANCE]/orders/$ORDER_ID` (with
     ``taler_pay_uri`` in the `StatusUnpaidResponse`), or
     :http:get:`[/instances/$INSTANCE]/private/orders/$ORDER_ID` with the
     ``taler_pay_uri`` in the `CheckPaymentUnpaidResponse`). That said,
     it is also possible to construct the URL by combining the base URL
     with the information from the `PostOrderResponse`.
     The API is structured this way since the payment redirect URL is not
     unique for every order: there might be varying parameters such as the
     session id.
 
   **Required permission:** ``orders-write``
 
   **Request:**
 
   The request must be a `PostOrderRequest`.
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The backend has successfully created the proposal.  The response is a
     :ts:type:`PostOrderResponse`.
   :http:statuscode:`404 Not found`:
     Possible reasons are:
 
     (1) The order given used products from the inventory, but those were
         not found in the inventory.
     (2) The merchant instance is unknown (including possibly the instance
         being not configured for new orders).
     (3) The wire method specified is not supported by the backend.
     (4) An OTP device ID was specified and is unknown.
 
     Details in the error code.
     NOTE: currently the client has no good way to find out which product
     is not in the inventory, we MAY want to specify that in the reply.
   :http:statuscode:`409 Conflict`:
     A different proposal already exists under the specified order ID,
     or the requested currency is not supported by this backend. Details in
     the error code.
   :http:statuscode:`410 Gone`:
     The order given used products from the inventory that are out of stock.
     The response is a :ts:type:`OutOfStockResponse`.
   :http:statuscode:`451 Unavailable for Legal Reasons`:
     The order could not be created because of legal
     reasons, specifically no exchange would accept
     a payment at this time because we have not yet
     satisfied the respective legal requirements.
     The :ref:`KYC status <merchantkycstatus>` API
     can be used to determine details about how to
     proceed with the KYC process.
     The body is a `PaymentDeniedLegallyResponse` with
     details about the exchange(s) causing the failure.
     Since protocol **v17**.
 
   **Details:**
 
   .. ts:def:: PostOrderRequest
 
     interface PostOrderRequest {
       // The order must at least contain the minimal
       // order detail, but can override all.
       order: Order;
 
       // If set, the backend will then set the refund deadline to the
       // payment deadline plus the specified delay.
       // If it's not set, the default value of the backend might be
       // used. Note that both this value and the backend default
       // will be ignored if ``refund_deadline`` is set in ``order``
       // as the ``refund_deadline`` takes precedence.
       // A value of "forever" is not allowed.
       refund_delay?: RelativeTime;
 
       // Specifies the payment target preferred by the client. Can be used
       // to select among the various (active) wire methods supported by the instance.
       payment_target?: string;
 
       // The session for which the payment is made (or replayed).
       // Only set for session-based payments.
       // Since protocol **v6**.
       session_id?: string;
 
       // Specifies that some products are to be included in the
       // order from the inventory.  For these inventory management
       // is performed (so the products must be in stock) and
       // details are completed from the product data of the backend.
       inventory_products?: MinimalInventoryProduct[];
 
       // Specifies a lock identifier that was used to
       // lock a product in the inventory.  Only useful if
       // ``inventory_products`` is set.  Used in case a frontend
       // reserved quantities of the individual products while
       // the shopping cart was being built.  Multiple UUIDs can
       // be used in case different UUIDs were used for different
       // products (i.e. in case the user started with multiple
       // shopping sessions that were combined during checkout).
       lock_uuids?: string[];
 
       // Should a token for claiming the order be generated?
       // False can make sense if the ORDER_ID is sufficiently
       // high entropy to prevent adversarial claims (like it is
       // if the backend auto-generates one). Default is 'true'.
       // Note: This is NOT related to tokens used for subscriptins or discounts.
       create_token?: boolean;
 
       // OTP device ID to associate with the order.
       // This parameter is optional.
       otp_id?: string;
     }
 
   The `Order` object represents the starting point for new `ContractTerms`.
   After validating and sanatizing all inputs, the merchant backend will add
   additional information to the order and create a new `ContractTerms` object
   that will be stored in the database.
 
   .. ts:def:: Order
 
     type Order = (OrderV1 | OrderV0) & OrderCommon;
 
   .. ts:def:: OrderV1
 
     interface OrderV1 {
       // Version 1 order support discounts and subscriptions.
       // https://docs.taler.net/design-documents/046-mumimo-contracts.html
       // @since protocol **v21**
       version: 1;
 
       // List of contract choices that the customer can select from.
       // @since protocol **v21**
       choices?: OrderChoice[];
     }
 
   .. ts:def:: OrderV0
 
     interface OrderV0 {
       // Optional, defaults to 0 if not set.
       version?: 0;
 
       // Total price for the transaction. The exchange will subtract deposit
       // fees from that amount before transferring it to the merchant.
       amount: Amount;
 
       // Maximum total deposit fee accepted by the merchant for this contract.
       // Overrides defaults of the merchant instance.
       max_fee?: Amount;
     }
 
   .. ts:def:: OrderCommon
 
     interface OrderCommon {
       // Human-readable description of the whole purchase.
       summary: string;
 
       // Map from IETF BCP 47 language tags to localized summaries.
       summary_i18n?: { [lang_tag: string]: string };
 
       // Unique identifier for the order. Only characters
       // allowed are "A-Za-z0-9" and ".:_-".
       // Must be unique within a merchant instance.
       // For merchants that do not store proposals in their DB
       // before the customer paid for them, the ``order_id`` can be used
       // by the frontend to restore a proposal from the information
       // encoded in it (such as a short product identifier and timestamp).
       order_id?: string;
 
       // URL where the same contract could be ordered again (if
       // available). Returned also at the public order endpoint
       // for people other than the actual buyer (hence public,
       // in case order IDs are guessable).
       public_reorder_url?: string;
 
       // See documentation of ``fulfillment_url`` field in `ContractTerms`.
       // Either fulfillment_url or fulfillment_message must be specified.
       // When creating an order, the fulfillment URL can
       // contain ``${ORDER_ID}`` which will be substituted with the
       // order ID of the newly created order.
       fulfillment_url?: string;
 
       // See documentation of ``fulfillment_message`` in `ContractTerms`.
       // Either ``fulfillment_url`` or ``fulfillment_message`` must be specified.
       fulfillment_message?: string;
 
       // Map from IETF BCP 47 language tags to localized fulfillment
       // messages.
       fulfillment_message_i18n?: { [lang_tag: string]: string };
 
       // Minimum age the buyer must have to buy.
       minimum_age?: Integer;
 
       // List of products that are part of the purchase.
       products?: Product[];
 
       // Time when this contract was generated. If null, defaults to current
       // time of merchant backend.
       timestamp?: Timestamp;
 
       // After this deadline has passed, no refunds will be accepted.
       // Overrides deadline calculated from ``refund_delay`` in
       // ``PostOrderRequest``.
       // A value of "never" is not allowed.
       refund_deadline?: Timestamp;
 
       // After this deadline, the merchant won't accept payments for the contract.
       // Overrides deadline calculated from default pay delay configured in
       // merchant backend.
       // A value of "never" is not allowed.
       pay_deadline?: Timestamp;
 
       // Transfer deadline for the exchange. Must be in the deposit permissions
       // of coins used to pay for this order.
       // Overrides deadline calculated from default wire transfer delay
       // configured in merchant backend. Must be after refund deadline.
       // A value of "never" is not allowed.
       wire_transfer_deadline?: Timestamp;
 
       // Base URL of the (public!) merchant backend API.
       // Must be an absolute URL that ends with a slash.
       // Defaults to the base URL this request was made to.
       merchant_base_url?: string;
 
       // Delivery location for (all!) products.
       delivery_location?: Location;
 
       // Time indicating when the order should be delivered.
       // May be overwritten by individual products.
       // Must be in the future.
       delivery_date?: Timestamp;
 
       // See documentation of ``auto_refund`` in ``ContractTerms``.
       // Specifies for how long the wallet should try to get an
       // automatic refund for the purchase.
       auto_refund?: RelativeTime;
 
       // Extra data that is only interpreted by the merchant frontend.
       // Useful when the merchant needs to store extra information on a
       // contract without storing it separately in their database.
       // Must really be an Object (not a string, integer, float or array).
       extra?: Object;
     }
 
 
   The `OrderChoice` object describes a possible choice within an order. The
   choice is done by the wallet and consists of in- and outputs. In the example
   of buying an article, the merchant could present the customer with the
   choice to use a valid subscription token or pay using a gift
   voucher. Available since protocol **v21**.
 
   .. ts:def:: OrderChoice
 
     interface OrderChoice {
       // Total price for the choice. The exchange will subtract deposit
       // fees from that amount before transferring it to the merchant.
       amount: Amount;
 
       // Human readable description of the semantics of the choice
       // within the contract to be shown to the user at payment.
       description?: string;
 
       // Map from IETF 47 language tags to localized descriptions.
       description_i18n?: { [lang_tag: string]: string };
 
       // Inputs that must be provided by the customer, if this choice is selected.
       // Defaults to empty array if not specified.
       inputs?: OrderInput[];
 
       // Outputs provided by the merchant, if this choice is selected.
       // Defaults to empty array if not specified.
       outputs?: OrderOutput[];
 
       // Maximum total deposit fee accepted by the merchant for this contract.
       // Overrides defaults of the merchant instance.
       max_fee?: Amount;
     }
 
   .. ts:def:: OrderInput
 
     // For now, only token inputs are supported.
     type OrderInput = OrderInputToken;
 
   .. ts:def:: OrderInputToken
 
     interface OrderInputToken {
 
       // Token input.
       type: "token";
 
       // Token family slug as configured in the merchant backend. Slug is unique
       // across all configured tokens of a merchant.
       token_family_slug: string;
 
       // How many units of the input are required.
       // Defaults to 1 if not specified. Output with count == 0 are ignored by
       // the merchant backend.
       count?: Integer;
 
     }
 
   .. ts:def:: OrderOutput
 
     type OrderOutput = OrderOutputToken | OrderOutputTaxReceipt;
 
   .. ts:def:: OrderOutputToken
 
     interface OrderOutputToken {
 
       // Token output.
       type: "token";
 
       // Token family slug as configured in the merchant backend. Slug is unique
       // across all configured tokens of a merchant.
       token_family_slug: string;
 
       // How many units of the output are issued by the merchant.
       // Defaults to 1 if not specified. Output with count == 0 are ignored by
       // the merchant backend.
       count?: Integer;
 
       // When should the output token be valid. Can be specified if the
       // desired validity period should be in the future (like selling
       // a subscription for the next month). Optional. If not given,
       // the validity is supposed to be "now" (time of order creation).
       valid_at?: Timestamp;
 
     }
 
   .. ts:def:: OrderOutputTaxReceipt
 
     interface OrderOutputTaxReceipt {
 
       // Tax receipt output.
       type: "tax-receipt";
 
     }
 
   The following `MinimalInventoryProduct` can be provided if the parts of the
   order are inventory-based, that is if the `PostOrderRequest` uses
   ``inventory_products``. For such products, which must be in the backend's inventory,
   the backend can automatically fill in the amount and other details about
   the product that are known to it from its ``products`` table.
   Note that the ``inventory_products`` will be appended to the
   list of ``products`` that the frontend already put into the ``order``.
   So if the frontend can sell additional non-inventory products together
   with ``inventory_products``.  Note that the backend will NOT update
   the ``amount`` of the ``order``, so the frontend must already have calculated
   the total price --- including the ``inventory_products``.
 
   .. ts:def:: MinimalInventoryProduct
 
     // Note that if the frontend does give details beyond these,
     // it will override those details (including price or taxes)
     // that the backend would otherwise fill in via the inventory.
     interface MinimalInventoryProduct {
 
       // Which product is requested (here mandatory!).
       product_id: string;
 
       // Legacy integer quantity. Deprecated; defaults to 1 if both
       // ``quantity`` and ``unit_quantity`` are absent.
       quantity?: Integer;
 
       // Preferred quantity string using "<integer>[.<fraction>]" syntax.
       unit_quantity?: string;
     }
 
   Supply either ``quantity`` or ``unit_quantity`` when referencing inventory products. If both are
   missing the backend assumes a quantity of one. ``unit_quantity`` follows the same decimal-string
   rules as ``unit_total_stock``.
 
   .. ts:def:: PostOrderResponse
 
     interface PostOrderResponse {
       // Order ID of the response that was just created.
       order_id: string;
 
       // Deadline when the offer expires; the customer must pay before.
       // @since protocol **v21**.
       pay_deadline: Timestamp;
 
       // Token that authorizes the wallet to claim the order.
       // Provided only if "create_token" was set to 'true'
       // in the request.
       token?: ClaimToken;
     }
 
   .. ts:def:: OutOfStockResponse
 
     interface OutOfStockResponse {
 
       // Product ID of an out-of-stock item.
       product_id: string;
 
       // Legacy integer quantity requested. Deprecated; see ``unit_requested_quantity``.
       requested_quantity: Integer;
 
       // Requested quantity using "<integer>[.<fraction>]" syntax with up to six fractional digits.
       unit_requested_quantity: string;
 
       // Legacy integer availability (must be below ``requested_quantity``).
       available_quantity: Integer;
 
       // Available quantity using "<integer>[.<fraction>]" syntax with up to six fractional digits.
       unit_available_quantity: string;
 
       // When do we expect the product to be again in stock?
       // Optional, not given if unknown.
       restock_expected?: Timestamp;
     }
 
 
 Inspecting orders
 ^^^^^^^^^^^^^^^^^
 
 .. http:get:: [/instances/$INSTANCE]/private/orders
 
   Returns known orders up to some point in the past.
 
   **Required permission:** ``orders-read``
 
   **Request:**
 
   :query paid: *Optional*. If set to yes, only return paid orders, if no only unpaid orders. Do not give (or use "all") to see all orders regardless of payment status.
   :query refunded: *Optional*. If set to yes, only return refunded orders, if no only unrefunded orders. Do not give (or use "all") to see all orders regardless of refund status.
   :query wired: *Optional*. If set to yes, only return wired orders, if no only orders with missing wire transfers. Do not give (or use "all") to see all orders regardless of wire transfer status.
   :query delta: *Optional*. takes value of the form ``N (-N)``, so that at most ``N`` values strictly older (younger) than ``start`` and ``date_s`` are returned.  Defaults to ``-20`` to return the last 20 entries (before ``start`` and/or ``date_s``).  Deprecated in protocol **v12**. Use *limit* instead.
   :query limit: *Optional*. At most return the given number of results. Negative for descending by row ID, positive for ascending by row ID. Default is ``20``.  Since protocol **v12**.
   :query date_s: *Optional.* Non-negative date in seconds after the UNIX Epoc, see ``delta`` for its interpretation.  If not specified, we default to the oldest or most recent entry, depending on ``limit``.
   :query start: *Optional*. Row number threshold, see ``limit`` for its interpretation.  Defaults to ``INT64_MAX``, namely the biggest row id possible in the database. Deprecated in protocol **v12**. Use *offset* instead.
   :query offset: *Optional*. Starting ``row_id`` for an iteration.  Since protocol **v12**.
   :query timeout_ms: *Optional*. Timeout in milliseconds to wait for additional orders if the answer would otherwise be negative (long polling). Only useful if ``limit`` is positive. Note that the merchant MAY still return a response that contains fewer than ``limit`` orders.
   :query session_id: *Optional*. Since protocol **v6**. Filters by session ID.
   :query fulfillment_url: *Optional*. Since protocol **v6**. Filters by fulfillment URL.
   :query summary_filter: *Optional*. Only returns orders where the summary contains the given text as a substring. Matching is case-insensitive. Since protocol **v23**.
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The response is an `OrderHistory`.
 
   **Details:**
 
   .. ts:def:: OrderHistory
 
     interface OrderHistory {
       // Timestamp-sorted array of all orders matching the query.
       // The order of the sorting depends on the sign of ``limit``.
       orders : OrderHistoryEntry[];
     }
 
 
   .. ts:def:: OrderHistoryEntry
 
     interface OrderHistoryEntry {
 
       // Order ID of the transaction related to this entry.
       order_id: string;
 
       // Row ID of the order in the database.
       row_id: Integer;
 
       // When the order was created.
       timestamp: Timestamp;
 
       // The amount of money the order is for. If the contract
       // has multiple choices and the user has not yet made a choice,
       // we return the amount of the first choice.
       amount: Amount;
 
       // The total amount of refunds granted by the merchant.
       // Includes refunds that the wallet did not yet pick up.
       // Only available if the order was paid.
       // Since **v24**.
       refund_amount: Amount;
 
       // The amount of refunds the customer's wallet did not yet
       // pick up.  Only available if the order was paid.
       // Since **v24**.
       pending_refund_amount: Amount;
 
       // The summary of the order.
       summary: string;
 
       // Whether some part of the order is refundable,
       // that is the refund deadline has not yet expired
       // and the total amount refunded so far is below
       // the value of the original transaction.
       refundable: boolean;
 
       // Whether the order has been paid or not.
       paid: boolean;
     }
 
 .. http:get:: [/instances/$INSTANCE]/private/orders/$ORDER_ID
 
   Merchant checks the payment status of an order.  If the order exists but is not paid
   and not claimed yet, the response provides a redirect URL.  When the user goes to this URL,
   they will be prompted for payment.  Differs from the ``public`` API both
   in terms of what information is returned and in that the wallet must provide
   the contract hash to authenticate, while for this API we assume that the
   merchant is authenticated (as the endpoint is not ``public``).
 
   **Required permission:** ``orders-read``
 
   **Request:**
 
   :query session_id: *Optional*. Session ID that the payment must be bound to.  If not specified, the payment is not session-bound.
   :query transfer: Deprecated in protocol **V6**. *Optional*. If set to "YES", try to obtain the wire transfer status for this order from the exchange. Otherwise, the wire transfer status MAY be returned if it is available.
   :query timeout_ms: *Optional*. Timeout in milliseconds to wait for a payment if the answer would otherwise be negative (long polling).
   :query allow_refunded_for_repurchase: *Optional*. Since protocol **v9** refunded orders are only returned under "already_paid_order_id" if this flag is set explicitly to "YES".
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     Returns a `MerchantOrderStatusResponse`, whose format can differ based on the status of the payment.
   :http:statuscode:`404 Not found`:
     The order or instance is unknown to the backend. Error code
     is set to either ``MERCHANT_GENERIC_ORDER_UNKNOWN`` or
     ``MERCHANT_GENERIC_INSTANCE_UNKNOWN``.
 
   **Details:**
 
   .. ts:def:: MerchantOrderStatusResponse
 
     type MerchantOrderStatusResponse = CheckPaymentPaidResponse |
                                        CheckPaymentClaimedResponse |
                                        CheckPaymentUnpaidResponse;
 
   .. ts:def:: CheckPaymentPaidResponse
 
     interface CheckPaymentPaidResponse {
       // The customer paid for this contract.
       order_status: "paid";
 
       // Was the payment refunded (even partially)?
       refunded: boolean;
 
       // True if there are any approved refunds that the wallet has
       // not yet obtained.
       refund_pending: boolean;
 
       // Did the exchange wire us the funds?
       wired: boolean;
 
       // Total amount the exchange deposited into our bank account
       // for this contract, excluding fees.
       deposit_total: Amount;
 
       // Numeric `error code <error-codes>` indicating errors the exchange
       // encountered tracking the wire transfer for this purchase (before
       // we even got to specific coin issues).
       // 0 if there were no issues.
       exchange_code: Integer;
 
       // HTTP status code returned by the exchange when we asked for
       // information to track the wire transfer for this purchase.
       // 0 if there were no issues.
       exchange_http_status: Integer;
 
       // Total amount that was refunded, 0 if refunded is false.
       refund_amount: Amount;
 
       // Contract terms.
       contract_terms: ContractTerms;
 
       // Index of the selected choice within the ``choices`` array of
       // ``contract terms``.
       // @since protocol **v21**
       choice_index?: Integer;
 
       // If the order is paid, set to the last time when a payment
       // was made to pay for this order. @since **v14**.
       last_payment: Timestamp;
 
       // The wire transfer status from the exchange for this order if
       // available, otherwise empty array.
       wire_details: TransactionWireTransfer[];
 
       // Reports about trouble obtaining wire transfer details,
       // empty array if no trouble were encountered.
       // @deprecated in protocol **v6**.
       wire_reports: TransactionWireReport[];
 
       // The refund details for this order.  One entry per
       // refunded coin; empty array if there are no refunds.
       refund_details: RefundDetails[];
 
       // Status URL, can be used as a redirect target for the browser
       // to show the order QR code / trigger the wallet.
       order_status_url: string;
     }
 
   .. ts:def:: CheckPaymentClaimedResponse
 
     interface CheckPaymentClaimedResponse {
       // A wallet claimed the order, but did not yet pay for the contract.
       order_status: "claimed";
 
       // Contract terms.
       contract_terms: ContractTerms;
 
       // Status URL, can be used as a redirect target for the browser
       // to show the order QR code / trigger the wallet.
       // Since protocol **v19**.
       order_status_url: string;
     }
 
   .. ts:def:: CheckPaymentUnpaidResponse
 
     interface CheckPaymentUnpaidResponse {
       // The order was neither claimed nor paid.
       order_status: "unpaid";
 
       // URI that the wallet must process to complete the payment.
       taler_pay_uri: string;
 
       // Time when the order was created.
       creation_time: Timestamp;
 
       // Deadline when the offer expires; the customer must pay before.
       // @since protocol **v21**.
       pay_deadline: Timestamp;
 
       // Order summary text.
       summary: string;
 
       // Total amount of the order (to be paid by the customer).
       // Will be undefined for unpaid v1 orders
       total_amount?: Amount;
 
       // Alternative order ID which was paid for already in the same session.
       // Only given if the same product was purchased before in the same session.
       already_paid_order_id?: string;
 
       // Fulfillment URL of an already paid order. Only given if under this
       // session an already paid order with a fulfillment URL exists.
       already_paid_fulfillment_url?: string;
 
       // Status URL, can be used as a redirect target for the browser
       // to show the order QR code / trigger the wallet.
       order_status_url: string;
 
       // We do we NOT return the contract terms here because they may not
       // exist in case the wallet did not yet claim them.
     }
 
   .. ts:def:: RefundDetails
 
     interface RefundDetails {
       // Reason given for the refund.
       reason: string;
 
       // True if a refund is still available for the wallet for this payment.
       pending: boolean;
 
       // When was the refund approved with a POST to
       // [/instances/$INSTANCE]/private/orders/$ORDER_ID/refund
       timestamp: Timestamp;
 
       // Total amount that was refunded (minus a refund fee).
       amount: Amount;
     }
 
   .. ts:def:: TransactionWireTransfer
 
     interface TransactionWireTransfer {
       // Responsible exchange.
       exchange_url: string;
 
       // 32-byte wire transfer identifier.
       wtid: Base32;
 
       // Execution time of the wire transfer.
       execution_time: Timestamp;
 
       // Total amount that has been wire transferred
       // to the merchant.
       amount: Amount;
 
       // Was this transfer confirmed by the merchant via the
       // POST /transfers API, or is it merely claimed by the exchange?
       confirmed: boolean;
     }
 
   .. ts:def:: TransactionWireReport
 
     interface TransactionWireReport {
       // Numerical `error code <error-codes>`.
       code: Integer;
 
       // Human-readable error description.
       hint: string;
 
       // Numerical `error code <error-codes>` from the exchange.
       exchange_code: Integer;
 
       // HTTP status code received from the exchange.
       exchange_http_status: Integer;
 
       // Public key of the coin for which we got the exchange error.
       coin_pub: CoinPublicKey;
     }
 
 
 
 .. _private-order-data-cleanup:
 
 Private order data cleanup
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 Some orders may contain sensitive information that the merchant may not want
 to retain after fulfillment, such as the customer's shipping address.  By
 initially labeling these order components as forgettable, the merchant can
 later tell the backend to forget those details (without changing the hash of
 the contract!) to minimize risks from information leakage.
 
 
 .. http:patch:: [/instances/$INSTANCE]/private/orders/$ORDER_ID/forget
 
   Forget fields in an order's contract terms that the merchant no
   longer needs.
 
   **Required permission:** ``orders-write``
 
   **Request:**
 
   The request must be a `forget request <ForgetRequest>`. The fields specified
   must have been marked as forgettable when the contract was created. Fields in
   the request that are not in the `contract terms <ContractTerms>` are ignored.
 
   A valid
   JSON path is defined as a string beginning with ``$.`` that follows the dot
   notation: ``$.wire_fee``, for example. The ``$`` represents the `contract terms <ContractTerms>`
   object, and an identifier following a ``.`` represents the field of that
   identifier belonging to the object preceding the dot. Arrays can be indexed
   by an non-negative integer within brackets: ``$.products[1]``. An asterisk ``*``
   can be used to index an array as a wildcard, which expands the path into a
   list of paths containing one path for
   each valid array index: ``$.products[*].description``. For a path to be valid,
   it must end with a reference to a field of an object (it cannot end with an
   array index or wildcard).
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The merchant deleted the specified fields from the contract of
     order $ORDER_ID.
   :http:statuscode:`204 No content`:
     The merchant had already deleted the specified fields
     from the contract of order $ORDER_ID.
   :http:statuscode:`400 Bad request`:
     The request is malformed or one of the paths is invalid.
   :http:statuscode:`404 Not found`:
     The merchant backend could not find the order or the instance
     and thus cannot process the forget request.
   :http:statuscode:`409 Conflict`:
     The request includes a field that was not marked as forgettable, so
     the merchant cannot delete that field.
 
   **Details:**
 
   .. ts:def:: ForgetRequest
 
     interface ForgetRequest {
 
       // Array of valid JSON paths to forgettable fields in the order's
       // contract terms.
       fields: string[];
     }
 
 
 .. http:delete:: [/instances/$INSTANCE]/private/orders/$ORDER_ID
 
   Delete information about an order.  Fails if the order was paid in the
   last 10 years (or whatever ``TAX_RECORD_EXPIRATION`` is set to) or was
   claimed but is unpaid and thus still a valid offer.
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The backend has successfully deleted the order.
   :http:statuscode:`404 Not found`:
     The backend does not know the instance or the order.
   :http:statuscode:`409 Conflict`:
     The backend refuses to delete the order.
 
 
 .. _merchant_refund:
 
 -----------------
 Approving Refunds
 -----------------
 
 .. http:post:: [/instances/$INSTANCE]/private/orders/$ORDER_ID/refund
 
   Increase the refund amount associated with a given order.  The user should be
   redirected to the ``taler_refund_uri`` to trigger refund processing in the wallet.
 
   **Required permission:** ``orders-refund``
 
   **Request:**
 
   The request body is a `RefundRequest` object.
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The refund amount has been increased, the backend
     responds with a `MerchantRefundResponse`.
   :http:statuscode:`403 Forbidden`:
     For the given order, the refund delay was zero and thus
     refunds are categorically not allowed.
   :http:statuscode:`404 Not found`:
     The order is unknown to the merchant.
   :http:statuscode:`410 Gone`:
     It is too late for aborting, the exchange may have already wired the funds
     to the merchant.
   :http:statuscode:`409 Conflict`:
     The refund amount exceeds the amount originally paid.
   :http:statuscode:`451 Unavailable for Legal Reasons`:
     The refund could not be awarded because of legal
     reasons (an exchange would refuse). The merchant
     staff needs to find another way to give a refund
     to the customer.
     The body is a `PaymentDeniedLegallyResponse` with
     details about the exchange causing the failure.
     Since protocol **v17**.
 
   **Details:**
 
   .. ts:def:: RefundRequest
 
     interface RefundRequest {
       // Amount to be refunded.
       refund: Amount;
 
       // Human-readable refund justification.
       reason: string;
     }
 
   .. ts:def:: MerchantRefundResponse
 
     interface MerchantRefundResponse {
 
       // URL (handled by the backend) that the wallet should access to
       // trigger refund processing.
       // taler://refund/...
       taler_refund_uri: string;
 
       // Contract hash that a client may need to authenticate an
       // HTTP request to obtain the above URI in a wallet-friendly way.
       h_contract: HashCode;
     }
 
 
 -----------------------
 Tracking Wire Transfers
 -----------------------
 
 This API is used by merchants that want to track the payments from the
 exchange to be sure that they have been paid on time. By telling the merchant
 backend about all incoming wire transfers, the backend can detect if an
 exchange failed to perform a wire transfer that was due.
 
 
 Informing the backend about incoming wire transfers
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 .. http:post:: [/instances/$INSTANCE]/private/transfers
 
   Inform the backend over an incoming wire transfer. The backend should inquire about the details with the exchange and mark the respective orders as wired.  Note that the request will fail if the WTID is not unique (which should be guaranteed by a correct exchange).
   This request is idempotent and should also be used to merely re-fetch the
   transfer information from the merchant's database (assuming we got a non-error
   response from the exchange before).
 
   **Required permission:** ``transfers-write``
 
   **Request:**
 
    The request must provide `transfer information <TransferInformation>`.
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The wire transfer is now confirmed at the merchant.
   :http:statuscode:`404 Not found`:
     The instance or account are unknown to the exchange.
   :http:statuscode:`409 Conflict`:
     The wire transfer identifier is already known to us, but for a different amount.
 
   **Details:**
 
   .. ts:def:: TransferInformation
 
     interface TransferInformation {
       // How much was wired to the merchant (minus fees).
       credit_amount: Amount;
 
       // Raw wire transfer identifier identifying the wire transfer (a base32-encoded value).
       wtid: WireTransferIdentifierRawP;
 
       // Full payto://-URI of the bank account that received the wire transfer.
       payto_uri: string;
 
       // Base URL of the exchange that made the wire transfer.
       exchange_url: string;
     }
 
 
 Querying known wire transfers
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 .. http:get:: [/instances/$INSTANCE]/private/transfers
 
   Obtain a list of all wire transfers the backend was told
   had been made into the merchant bank account.
   Since protocol **v20** this endpoint is only about
   actually confirmed wire transfers.
 
   **Required permission:** ``transfers-read``
 
   **Request:**
 
   :query payto_uri: *Optional*. Full payto://-URI to filter for transfers to the given bank account (subject and amount MUST NOT be given in the payto:// URI).  Note that the URI must be URL-encoded.
 
   :query before: *Optional*. Filter for transfers executed before the given timestamp.
 
   :query after: *Optional*. Filter for transfers executed after the given timestamp.
 
   :query limit: *Optional*. At most return the given number of results. Negative for descending in execution time, positive for ascending in execution time. Default is ``-20``.
 
   :query offset: *Optional*. Starting ``transfer_serial_id`` for an iteration.
 
   :query expected: *Optional*. Filter transfers that we expected to receive (YES: only expected, NO: only unexpected, ALL: default). Since protocol **v20**.
 
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The body of the response is a `TransferList`.
 
   **Details:**
 
   .. ts:def:: TransferList
 
     interface TransferList {
        // List of all the transfers that fit the filter that we know.
        transfers : TransferDetails[];
     }
 
   .. ts:def:: TransferDetails
 
     interface TransferDetails {
       // How much was wired to the merchant (minus fees).
       credit_amount: Amount;
 
       // Raw wire transfer identifier identifying the wire transfer (a base32-encoded value).
       wtid: WireTransferIdentifierRawP;
 
       // Full payto://-URI of the bank account that received the wire transfer.
       payto_uri: string;
 
       // Base URL of the exchange that made the wire transfer.
       exchange_url: string;
 
       // Serial number identifying the transfer in the merchant backend.
       // Used for filtering via ``offset``.
       transfer_serial_id: Integer;
 
       // Time of the execution of the wire transfer.
       execution_time: Timestamp;
 
       // True if we checked the exchange's answer and are happy with it.
       // False if we have an answer and are unhappy, missing if we
       // do not have an answer from the exchange.
       // Removed in protocol **v20**.
       verified?: boolean;
 
       // True if the merchant uses the POST /transfers API to confirm
       // that this wire transfer took place (and it is thus not
       // something merely claimed by the exchange).
       // Removed in protocol **v20**.
       confirmed?: boolean;
 
       // True if this wire transfer was expected.
       // (a matching "/private/incoming" record exists).
       // Since protocol **v20**.
       expected?: boolean;
     }
 
 
 
 Querying expected wire transfers
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 .. http:get:: [/instances/$INSTANCE]/private/incoming
 
   Obtain a list of expected incoming wire transfers the backend is
   anticipating.
   Since protocol **v20**.
 
   **Required permission:** ``transfers-read``
 
   **Request:**
 
   :query payto_uri: *Optional*. Full payto://-URI to filter for transfers to the given bank account (subject and amount MUST NOT be given in the payto:// URI).  Note that the URI must be URL-encoded.
 
   :query before: *Optional*. Filter for transfers executed before the given timestamp.
 
   :query after: *Optional*. Filter for transfers executed after the given timestamp.
 
   :query limit: *Optional*. At most return the given number of results. Negative for descending in execution time, positive for ascending in execution time. Default is ``-20``.
 
   :query offset: *Optional*. Starting ``transfer_serial_id`` for an iteration.
 
   :query verified: *Optional*. Filter transfers by verification status (YES: reconcilation worked, NO: reconciliation failed, ALL: default)
 
   :query confirmed: *Optional*. Filter transfers that were confirmed (YES: credit confirmed, NO: credit still pending, ALL: default)
 
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The body of the response is a `ExpectedTransferList`.
 
   **Details:**
 
   .. ts:def:: ExpectedTransferList
 
     interface ExpectedTransferList {
        // List of all the expected incoming transfers that fit the
        // filter that we know.
        incoming : ExpectedTransferDetails[];
     }
 
   .. ts:def:: ExpectedTransferDetails
 
     interface ExpectedTransferDetails {
       // How much should be wired to the merchant (minus fees).
       expected_credit_amount?: Amount;
 
       // Raw wire transfer identifier identifying the wire transfer (a base32-encoded value).
       wtid: WireTransferIdentifierRawP;
 
       // Full payto://-URI of the bank account that received the wire transfer.
       payto_uri: string;
 
       // Base URL of the exchange that made the wire transfer.
       exchange_url: string;
 
       // Serial number identifying the expected transfer in the backend.
       // Used for filtering via ``offset``.
       expected_transfer_serial_id: Integer;
 
       // Expected time of the execution of the wire transfer
       // by the exchange, according to the exchange.
       execution_time?: Timestamp;
 
       // True if we checked the exchange's answer and are happy with
       // the reconciation data.
       // False if we have an answer and are unhappy, missing if we
       // do not have an answer from the exchange.
       // Does not imply that the wire transfer was settled (for
       // that, see ``confirmed``).
       validated: boolean;
 
       // True if the merchant uses the POST /transfers API to confirm
       // that this wire transfer took place (and it is thus not
       // something merely claimed by the exchange).
       // (a matching entry exists in /private/transfers)
       confirmed: boolean;
 
       // Last HTTP status we received from the exchange, 0 for
       // none (incl. timeout)
       last_http_status: Integer;
 
       // Last Taler error code we got from the exchange.
       last_ec: ErrorCode;
 
       // Last error detail we got back from the exchange.
       last_error_detail?: string;
     }
 
 
 Deleting confirmed wire transfer
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 Deleting a wire transfer can be useful in case of a data entry
 mistake. In particular, if the exchange base URL was entered
 badly, deleting the old entry and adding a correct one is a
 good idea. Note that deleting wire transfers is not possible
 if they were expected.
 
 .. http:delete:: [/instances/$INSTANCE]/private/transfers/$TID
 
    Here, the TID is the 'transfer_serial_id' of the transfer
    to delete.
 
   **Required permission:** ``transfers-write``
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The transfer was deleted.
   :http:statuscode:`404 Not found`:
     The transfer was already unknown.
   :http:statuscode:`409 Conflict`:
     The transfer cannot be deleted anymore.
 
 
 -----------
 OTP Devices
 -----------
 
 OTP devices can be used to allow offline merchants
 to validate that a customer made a payment.
 
 
 .. http:post:: [/instances/$INSTANCE]/private/otp-devices
 
   This is used to associate an OTP device with an instance.
 
   **Required permission:** ``otp-devices-write``
 
   **Request:**
 
   The request must be a `OtpDeviceAddDetails`.
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The creation of the template is successful.
   :http:statuscode:`404 Not found`:
     The merchant instance is unknown or it is not in our data.
 
   **Details:**
 
   .. ts:def:: OtpDeviceAddDetails
 
     interface OtpDeviceAddDetails {
 
       // Device ID to use.
       otp_device_id: string;
 
       // Human-readable description for the device.
       otp_device_description: string;
 
       // A key encoded with RFC 3548 Base32.
       // IMPORTANT: This is not using the typical
       // Taler base32-crockford encoding.
       // Instead it uses the RFC 3548 encoding to
       // be compatible with the TOTP standard.
       otp_key: string;
 
       // Algorithm for computing the POS confirmation.
       // "NONE" or 0: No algorithm (no pos confirmation will be generated)
       // "TOTP_WITHOUT_PRICE" or 1: Without amounts (typical OTP device)
       // "TOTP_WITH_PRICE" or 2: With amounts (special-purpose OTP device)
       // The "String" variants are supported @since protocol **v7**.
       otp_algorithm: Integer | string;
 
       // Counter for counter-based OTP devices.
       otp_ctr?: Integer;
     }
 
 
 .. http:patch:: [/instances/$INSTANCE]/private/otp-devices/$DEVICE_ID
 
   This is used to update an OTP device. It is useful when we need to change information in the OTP device or when we have mistake some information.
 
   **Required permission:** ``otp-devices-write``
 
   **Request:**
 
   The request must be a `OtpDevicePatchDetails`.
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The template has successfully modified.
   :http:statuscode:`404 Not found`:
     The template(ID) is unknown to the backend.
   :http:statuscode:`409 Conflict`:
     The provided information is inconsistent with the current state of the template. Changes made is the same with
     another store.
 
   **Details:**
 
   .. ts:def:: OtpDevicePatchDetails
 
    interface OtpDevicePatchDetails {
 
      // Human-readable description for the device.
      otp_device_description: string;
 
      // A key encoded with RFC 3548 Base32.
      // IMPORTANT: This is not using the typical
      // Taler base32-crockford encoding.
      // Instead it uses the RFC 3548 encoding to
      // be compatible with the TOTP standard.
      otp_key?: string;
 
      // Algorithm for computing the POS confirmation.
      otp_algorithm: Integer;
 
      // Counter for counter-based OTP devices.
      otp_ctr?: Integer;
    }
 
 
 .. http:get:: [/instances/$INSTANCE]/private/otp-devices
 
   This is used to return the list of all the OTP devices.
 
   **Required permission:** ``otp-devices-read``
 
   **Response:**
 
   :http:statuscode:`200 OK`:
      The backend has successfully returned all the templates. Returns a `OtpDeviceSummaryResponse`.
   :http:statuscode:`404 Not found`:
      The backend has does not know about the instance.
 
   **Details:**
 
   .. ts:def:: OtpDeviceSummaryResponse
 
     interface OtpDeviceSummaryResponse {
 
       // Array of devices that are present in our backend.
       otp_devices: OtpDeviceEntry[];
     }
 
   .. ts:def:: OtpDeviceEntry
 
     interface OtpDeviceEntry {
 
       // Device identifier.
       otp_device_id: string;
 
       // Human-readable description for the device.
       device_description: string;
     }
 
 .. http:get:: [/instances/$INSTANCE]/private/otp-devices/$DEVICE_ID
 
   This is used to obtain detailed information about a specific OTP device.
 
   The client can provide additional inputs in the query to allow the backend
   to compute and return a sample OTP code.  Note that it is not an error if
   the client provides query arguments that are not being used *or* that are
   insufficient for the server to compute the ``otp_code``: If the client
   provides inadequate query parameters, the ``otp_code`` is simply omitted
   from the response.
 
   **Required permission:** ``otp-devices-read``
 
   **Query:**
 
   :query faketime=TIMESTAMP: *Optional*. Timestamp in seconds to use when calculating the current OTP code of the device. Since protocol **v10**.
   :query price=AMOUNT: *Optional*. Price to use when calculating the current OTP code of the device. Since protocol **v10**.
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The backend has successfully returned the detailed information about a specific OTP device.
     Returns a `OtpDeviceDetails`.
   :http:statuscode:`404 Not found`:
     The OTP device or instance is unknown to the backend.
 
   **Details:**
 
   .. ts:def:: OtpDeviceDetails
 
     interface OtpDeviceDetails {
 
       // Human-readable description for the device.
       device_description: string;
 
       // Algorithm for computing the POS confirmation.
       //
       // Currently, the following numbers are defined:
       // 0: None
       // 1: TOTP without price
       // 2: TOTP with price
       otp_algorithm: Integer;
 
       // Counter for counter-based OTP devices.
       otp_ctr?: Integer;
 
       // Current time for time-based OTP devices.
       // Will match the ``faketime`` argument of the
       // query if one was present, otherwise the current
       // time at the backend.
       //
       // Available since protocol **v10**.
       otp_timestamp: Integer;
 
       // Current OTP confirmation string of the device.
       // Matches exactly the string that would be returned
       // as part of a payment confirmation for the given
       // amount and time (so may contain multiple OTP codes).
       //
       // If the ``otp_algorithm`` is time-based, the code is
       // returned for the current time, or for the ``faketime``
       // if a TIMESTAMP query argument was provided by the client.
       //
       // When using OTP with counters, the counter is **NOT**
       // increased merely because this endpoint created
       // an OTP code (this is a GET request, after all!).
       //
       // If the ``otp_algorithm`` requires an amount, the
       // ``amount`` argument must be specified in the
       // query, otherwise the ``otp_code`` is not
       // generated.
       //
       // This field is *optional* in the response, as it is
       // only provided if we could compute it based on the
       // ``otp_algorithm`` and matching client query arguments.
       //
       // Available since protocol **v10**.
       otp_code?: string;
 
    }
 
 .. http:delete:: [/instances/$INSTANCE]/private/otp-devices/$DEVICE_ID
 
   **Required permission:** ``otp-devices-write``
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The backend has successfully deleted the OTP device.
   :http:statuscode:`404 Not found`:
     The backend does not know the instance or the OTP device.
 
 
 .. _merchant-template-api:
 
 ---------
 Templates
 ---------
 
 The template is a backend feature that is used to allow wallets to create an
 order. This is useful in cases where a store does not have Internet
 connectivity or where a Web site wants to enable payments on a purely static
 Web page (for example to collect donations). In these cases, the GNU Taler
 wallet can be used to setup an order (and then of course pay for it).
 
 The template itself primarily provides order details that cannot be be changed
 by the customer when the wallet creates the order.  The idea is that the user
 *may* be prompted to enter certain information, such as the amount to be paid,
 or the order summary (as a reminder to themselves or a message to the store),
 while the template provides all of the other contract details.
 
 The typical user-experience with templatates is that the user first scans a QR
 code or clicks on a taler://-URI which contains a ``pay-template`` (see `LSD
 0006 <https://lsd.gnunet.org/lsd0006/>`__). The URI specifies which values the
 user should supply, currently either nothing, the amount, the order summary or
 both.  The URI may also specify defaults or partial defaults for those
 values. After the user has supplied those values, the wallet will use the
 public template API to create the order, then fetch the order details, and
 proceed as if it had been given the respective ``pay`` URI in the first place:
 show the full contract details and allow the user to make a payment.  If the
 user chooses to aborts the payment, the wallet should give the user the
 opportunity to edit the values and create another order with different values.
 If the template does not include any values that the user is allowed to edit
 (so it is basically a fixed contract), the wallet should directly create the
 order and immediately proceed to the contract acceptance dialog.
 
 The business process for the templating API is also pretty simple. First, the
 private API is used to setup (or edit) the template, providing all of the
 contract terms that subsequently cannot be changed by the customer/wallet.
 This template data is then stored under the template ID which can be freely
 chosen and must be in URL-encoded format. The SPA should also make it easy
 for the merchant to convert the template ID into a taler://-URI and/or QR code.
 Here, the merchant must additionally specify the defaults (if any) for the
 customer-editable values. Afterwards, the merchant can print out the QR code
 for display at the store, add a link to the taler://-URI and/or embed the
 respective QR-code image into their Web page.
 
 To receive a payment confirmation, the mechant may choose to configure a
 webhook in the merchant backend on the ``pay`` action, for example to send an
 SMS to their mobile phone.  For points-of-sale without a mobile phone or
 Internet connectivity, the OTP mechanism can also be used to confirm payments.
 
 
 
 Adding templates
 ^^^^^^^^^^^^^^^^
 
 .. http:post:: [/instances/$INSTANCE]/private/templates
 
   This is used to create a template.
 
   **Required permission:** ``templates-write``
 
   **Request:**
 
   The request must be a `TemplateAddDetails`.
 
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The creation of the template is successful.
   :http:statuscode:`404 Not found`:
     The merchant instance is unknown or it is not in our data.
 
   **Details:**
 
 
   .. ts:def:: TemplateAddDetails
 
     interface TemplateAddDetails {
 
       // Template ID to use.
       template_id: string;
 
       // Human-readable description for the template.
       template_description: string;
 
       // OTP device ID.
       // This parameter is optional.
       otp_id?: string;
 
       // Fixed contract information for orders created from
       // this template.
       template_contract: TemplateContractDetails;
 
       // Key-value pairs matching a subset of the
       // fields from ``template_contract`` that are
       // user-editable defaults for this template.
       // Since protocol **v13**.
       editable_defaults?: Object;
     }
 
 
   .. ts:def:: TemplateContractDetails
 
     interface TemplateContractDetails {
 
       // Human-readable summary for the template.
       summary?: string;
 
       // Required currency for payments to the template.
       // The user may specify any amount, but it must be
       // in this currency.
       // This parameter is optional and should not be present
       // if "amount" is given.
       currency?: string;
 
       // The price is imposed by the merchant and cannot be changed by the customer.
       // This parameter is optional.
       amount?: Amount;
 
       // Minimum age buyer must have (in years). Default is 0.
       minimum_age: Integer;
 
       // The time the customer need to pay before his order will be deleted.
       // It is deleted if the customer did not pay and if the duration is over.
       pay_duration: RelativeTime;
 
    }
 
 
 
 Editing templates
 ^^^^^^^^^^^^^^^^^
 
 
 .. http:patch:: [/instances/$INSTANCE]/private/templates/$TEMPLATE_ID
 
   This is used to update a template. It is useful when we need to change information in the template or when we have mistake some information.
 
   **Required permission:** ``templates-write``
 
   **Request:**
 
   The request must be a `TemplatePatchDetails`.
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The template has successfully modified.
   :http:statuscode:`404 Not found`:
     The template(ID) is unknown to the backend.
   :http:statuscode:`409 Conflict`:
     The provided information is inconsistent with the current state of the template. Changes made is the same with
     another store.
 
   **Details:**
 
 
   .. ts:def:: TemplatePatchDetails
 
     interface TemplatePatchDetails {
 
       // Human-readable description for the template.
       template_description: string;
 
       // OTP device ID.
       // This parameter is optional.
       otp_id?: string;
 
       // Additional information in a separate template.
       template_contract: TemplateContractDetails;
 
       // Key-value pairs matching a subset of the
       // fields from ``template_contract`` that are
       // user-editable defaults for this template.
       // Since protocol **v13**.
       editable_defaults?: Object;
    }
 
 
 
 Inspecting template
 ^^^^^^^^^^^^^^^^^^^
 
 .. http:get:: [/instances/$INSTANCE]/private/templates
 
   This is used to return the list of all the templates.
 
 
   **Required permission:** ``templates-read``
 
   **Response:**
 
   :http:statuscode:`200 OK`:
      The backend has successfully returned all the templates. Returns a `TemplateSummaryResponse`.
   :http:statuscode:`404 Not found`:
      The backend has does not know about the instance.
 
   **Details:**
 
   .. ts:def:: TemplateSummaryResponse
 
     interface TemplateSummaryResponse {
 
       // List of templates that are present in our backend.
       templates: TemplateEntry[];
     }
 
   The `TemplateEntry` object describes a template. It has the following structure:
 
   .. ts:def:: TemplateEntry
 
     interface TemplateEntry {
 
       // Template identifier, as found in the template.
       template_id: string;
 
       // Human-readable description for the template.
       template_description: string;
 
     }
 
 .. http:get:: [/instances/$INSTANCE]/private/templates/$TEMPLATE_ID
 
   This is used to obtain detailed information about a specific template.
 
 
   **Required permission:** ``templates-read``
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The backend has successfully returned the detailed information about a specific template.
     Returns a `TemplateDetails`.
   :http:statuscode:`404 Not found`:
     The instance or template(ID) is unknown to the backend.
 
   **Details:**
 
 
   .. ts:def:: TemplateDetails
 
     interface TemplateDetails {
 
       // Human-readable description for the template.
       template_description: string;
 
       // OTP device ID.
       // This parameter is optional.
       otp_id?: string;
 
       // Additional information in a separate template.
       template_contract: TemplateContractDetails;
 
       // Key-value pairs matching a subset of the
       // fields from ``template_contract`` that are
       // user-editable defaults for this template.
       // Since protocol **v13**.
       editable_defaults?: Object;
 
       // Required currency for payments.  Useful if no
       // amount is specified in the ``template_contract``
       // but the user should be required to pay in a
       // particular currency anyway.  Merchant backends
       // may reject requests if the ``template_contract``
       // or ``editable_defaults`` do
       // specify an amount in a different currency.
       // This parameter is optional.
       // Since protocol **v13**.
       required_currency?: string;
     }
 
 
 
 Removing template
 ^^^^^^^^^^^^^^^^^
 
 .. http:delete:: [/instances/$INSTANCE]/private/templates/$TEMPLATE_ID
 
   This is used to delete information about a template. If we no longer use it.
 
   **Required permission:** ``templates-write``
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The backend has successfully deleted the template.
   :http:statuscode:`404 Not found`:
     The backend does not know the instance or the template.
 
 
 
 Using template
 ^^^^^^^^^^^^^^
 
 .. http:get:: [/instances/$INSTANCE]/templates/$TEMPLATE_ID
 
   This is used to obtain information about a specific template by wallets
   before they ask the user to fill in details.
   This endpoint is available since protocol **v11**.
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The backend has successfully returned the detailed information about a specific template.
     Returns a `WalletTemplateDetails`.
   :http:statuscode:`404 Not found`:
     The instance or template(ID) is unknown to the backend.
 
   **Details:**
 
   .. ts:def:: WalletTemplateDetails
 
     interface WalletTemplateDetails {
 
       // Hard-coded information about the contrac terms
       // for this template.
       template_contract: TemplateContractDetails;
 
       // Key-value pairs matching a subset of the
       // fields from ``template_contract`` that are
       // user-editable defaults for this template.
       // Since protocol **v13**.
       editable_defaults?: Object;
 
       // Required currency for payments.  Useful if no
       // amount is specified in the ``template_contract``
       // but the user should be required to pay in a
       // particular currency anyway.  Merchant backends
       // may reject requests if the ``template_contract``
       // or ``editable_defaults`` do
       // specify an amount in a different currency.
       // This parameter is optional.
       // Since protocol **v13**.
       required_currency?: string;
     }
 
 
 .. http:post:: [/instances/$INSTANCES]/templates/$TEMPLATE_ID
 
   This using template can be modified by everyone and will be used to create order.
 
 
   **Request:**
 
   The request must be a `UsingTemplateDetails` and we accept JSON application and URL encoded.
 
 
   **Response:**
 
   The response is exactly the same type of response as when
   creating an order using :ref:`POST /private/orders <post-order>`.
 
   **Details:**
 
   .. ts:def:: UsingTemplateDetails
 
     interface UsingTemplateDetails {
 
       // Summary of the template
       summary?: string;
 
       // The amount entered by the customer.
       amount?: Amount;
     }
 
 
 --------
 Webhooks
 --------
 
 The webhook is a backend feature that is used to send a confirmation to the merchant. It can be send with a SMS, email or with another method. It will confirm that the
 customer paid the merchant. It will show the date and the price the customer paid. For details on setup and supported event payloads, see the
 `Merchant manual – Setting up a webhook <https://docs.taler.net/taler-merchant-manual.html#setting-up-a-webhook>`_.
 
 Each webhook is bound to an ``event_type``. The backend currently recognizes the following types, which are mirrored in the ``WebhookEventType`` enum so API clients can
 validate their payloads without guesswork:
 
 .. ts:def:: WebhookEventType
 
    enum WebhookEventType {
       ORDER_CREATED = "order_created",
       PAY = "pay",
       REFUND = "refund",
       ORDER_SETTLED = "order_settled",
       CATEGORY_ADDED = "category_added",
       CATEGORY_UPDATED = "category_updated",
       CATEGORY_DELETED = "category_deleted",
       INVENTORY_ADDED = "inventory_added",
       INVENTORY_UPDATED = "inventory_updated",
       INVENTORY_DELETED = "inventory_deleted"
    }
 
 - ``order_created``: fired whenever a new order is created and exposes the ``order_id``, contract, and owning ``instance_id``.
 - ``pay``: emitted after a payment succeeds; the payload contains the paid contract terms and ``order_id``.
 - ``refund``: triggered when a refund is approved and includes timestamp, refunded amount, and reason.
 - ``order_settled``: sent when reconciliation links a wire transfer to an order (includes ``order_id`` and ``wtid``).
 - ``category_added`` / ``category_updated`` / ``category_deleted``: cover lifecycle changes to product categories.
 - ``inventory_added`` / ``inventory_updated`` / ``inventory_deleted``: cover lifecycle changes to inventory items, including descriptive fields and stock state.
 
 For the full payloads associated with each event consult the merchant manual section linked above.
 
 
 
 Adding webhooks
 ^^^^^^^^^^^^^^^
 
 .. http:post:: [/instances/$INSTANCES]/private/webhooks
 
   This is used to create a webhook.
 
   **Required permission:** ``webhooks-write``
 
   **Request:**
 
   The request must be a `WebhookAddDetails`.
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The creation of the webhook is successsful.
 
   :http:statuscode:`404 Not found`:
     The merchant instance is unknown or it not in our data.
 
   **Details:**
 
   .. ts:def:: WebhookAddDetails
 
     interface WebhookAddDetails {
 
       // Webhook ID to use.
       webhook_id: string;
 
       // The event of the webhook: why the webhook is used.
       event_type: WebhookEventType;
 
       // URL of the webhook where the customer will be redirected.
       url: string;
 
       // Method used by the webhook
       http_method: string;
 
       // Header template of the webhook
       header_template?: string;
 
       // Body template by the webhook
       body_template?: string;
 
    }
 
 
 Editing webhooks
 ^^^^^^^^^^^^^^^^
 
 .. http:patch:: [/instances/$INSTANCES]/private/webhooks/$WEBHOOK_ID
 
   This is used to update a webhook.
 
   **Required permission:** ``webhooks-write``
 
   **Request:**
 
   The request must be a `WebhookPatchDetails`.
 
   **Response:**
 
   :http:statuscode:`204 No content`:
      The webhook has successfully modified.
   :http:statuscode:`404 Not found`:
      The webhook(ID) is unknown to the backend.
   :http:statuscode:`409 Conflict`:
      The provided information is inconsistent with the current state of the webhook. Changes made is the same with another store.
 
   **Details:**
 
   .. ts:def:: WebhookPatchDetails
 
     interface WebhookPatchDetails {
 
       // The event of the webhook: why the webhook is used.
       event_type: WebhookEventType;
 
       // URL of the webhook where the customer will be redirected.
       url: string;
 
       // Method used by the webhook
       http_method: string;
 
       // Header template of the webhook
       header_template?: string;
 
       // Body template by the webhook
       body_template?: string;
 
    }
 
 
 
 Inspecting webhook
 ^^^^^^^^^^^^^^^^^^
 
 .. http:get:: [/instances/$INSTANCES]/private/webhooks
 
   This is used to return all the webhooks that are present in our backend.
 
   **Required permission:** ``webhooks-read``
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The backend has successfully returned all the webhooks. Returns a `WebhookSummaryResponse`.
 
   :http:statuscode:`404 Not found`:
     The backend has does not know about the instance.
 
   **Details:**
 
   .. ts:def:: WebhookSummaryResponse
 
     interface WebhookSummaryResponse {
 
       // Return webhooks that are present in our backend.
       webhooks: WebhookEntry[];
 
    }
 
   The `WebhookEntry` object describes a webhook. It has the following structure:
 
   .. ts:def:: WebhookEntry
 
     interface WebhookEntry {
 
       // Webhook identifier, as found in the webhook.
       webhook_id: string;
 
       // The event of the webhook: why the webhook is used.
       event_type: WebhookEventType;
 
    }
 
 
 .. http:get:: [/instances/$INSTANCES]/private/webhooks/$WEBHOOK_ID
 
   This is used to obtain detailed information about apecific template.
 
   **Required permission:** ``webhooks-read``
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The backend has successfully returned the detailed information about a specific webhook. Returns a `WebhookDetails`.
 
   :http:statuscode:`404 Not found`:
     The webhook(ID) is unknown to the backend.
 
   **Details:**
 
   .. ts:def:: WebhookDetails
 
     interface WebhookDetails {
 
       // The event of the webhook: why the webhook is used.
       event_type: WebhookEventType;
 
       // URL of the webhook where the customer will be redirected.
       url: string;
 
       // Method used by the webhook
       http_method: string;
 
       // Header template of the webhook
       header_template?: string;
 
       // Body template by the webhook
       body_template?: string;
 
    }
 
 
 Removing webhook
 ^^^^^^^^^^^^^^^^
 
 .. http:delete:: [/instances/$INSTANCES]/private/webhooks/$WEBHOOK_ID
 
   This is used to delete information about a webhook.
 
   **Required permission:** ``webhooks-write``
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The backend has successfully deleted the webhook.
 
   :http:statuscode:`404 Not found`:
     The webhook(ID) or the instance is unknown to the backend.
 
 
 
 ----------------------------------------
 Token Families: Subscriptions, Discounts
 ----------------------------------------
 
 This API provides functionalities for the issuance, management, and revocation
 of token families. Tokens facilitate the implementation of subscriptions and
 discounts, engaging solely the merchant and the user. Each token family
 encapsulates details pertaining to its respective tokens, guiding the merchant's
 backend on the appropriate processing and handling.
 
 
 Creating token families
 ^^^^^^^^^^^^^^^^^^^^^^^
 
 .. http:post:: [/instances/$INSTANCES]/private/tokenfamilies
 
   This is used to create a token family.
 
   **Required permission:** ``tokenfamilies-write``
 
   **Request:**
 
   The request must be a `TokenFamilyCreateRequest`.
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The token family was created successfully.
 
   :http:statuscode:`404 Not found`:
     The merchant backend is unaware of the instance.
 
   **Details:**
 
   .. ts:def:: TokenFamilyCreateRequest
 
     interface TokenFamilyCreateRequest {
 
       // Identifier for the token family consisting of unreserved characters
       // according to RFC 3986.
       slug: string;
 
       // Human-readable name for the token family.
       name: string;
 
       // Human-readable description for the token family.
       description: string;
 
       // Optional map from IETF BCP 47 language tags to localized descriptions.
       description_i18n?: { [lang_tag: string]: string };
 
       // Additional meta data, such as the ``trusted_domains``
       // or ``expected_domains``. Depends on the ``kind``.
       extra_data?: object;
 
       // Start time of the token family's validity period.
       // If not specified, merchant backend will use the current time.
       valid_after?: Timestamp;
 
       // End time of the token family's validity period.
       valid_before: Timestamp;
 
       // Validity duration of an issued token.
       duration: RelativeTime;
 
       // Rounding granularity for the start validity of keys.
       // The desired time is rounded down to a multiple of this
       // granularity and then the ``start_offset`` is added to
       // compute the actual start time of the token keys' validity.
       // The end is then computed by adding the ``duration``.
       // Must be 1 minute, 1 hour, 1 day, 1 week, 30 days, 90 days
       // or 365 days (1 year).
       validity_granularity: RelativeTime;
 
       // Offset to subtract from the start time rounded to ``validity_granularity``
       // to compute the actual start time for a key.
       // Default is zero.
       start_offset: RelativeTime;
 
       // Kind of the token family.
       kind: TokenFamilyKind;
 
    }
 
   .. ts:def:: TokenFamilyKind
 
     enum TokenFamilyKind {
       Discount = "discount",
       Subscription = "subscription",
     }
 
 
 Updating token families
 ^^^^^^^^^^^^^^^^^^^^^^^
 
 .. http:patch:: [/instances/$INSTANCES]/private/tokenfamilies/$TOKEN_FAMILY_SLUG
 
   This is used to update a token family.
 
   **Required permission:** ``tokenfamilies-write``
 
   **Request:**
 
   The request must be a `TokenFamilyUpdateRequest`.
 
   **Response:**
 
   :http:statuscode:`204 No Content`:
     The token family was successsful updated.
 
   :http:statuscode:`404 Not found`:
     The merchant backend is unaware of the token family or instance.
 
   **Details:**
 
   .. ts:def:: TokenFamilyUpdateRequest
 
     interface TokenFamilyUpdateRequest {
 
       // Human-readable name for the token family.
       name: string;
 
       // Human-readable description for the token family.
       description: string;
 
       // Optional map from IETF BCP 47 language tags to localized descriptions.
       description_i18n: { [lang_tag: string]: string };
 
       // Additional meta data, such as the ``trusted_domains``
       // or ``expected_domains``. Depends on the ``kind``.
       extra_data?: object;
 
       // Start time of the token family's validity period.
       valid_after: Timestamp;
 
       // End time of the token family's validity period.
       valid_before: Timestamp;
 
    }
 
 
 
 Inspecting token families
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 .. http:get:: [/instances/$INSTANCES]/private/tokenfamilies
 
   This is used to list all configured token families for an instance.
 
   **Required permission:** ``tokenfamilies-read``
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The merchant backend has successfully returned all token families.
     Returns a `TokenFamiliesList`.
 
   :http:statuscode:`404 Not found`:
     The merchant backend is unaware of the instance.
 
   **Details:**
 
   .. ts:def:: TokenFamiliesList
 
     // TODO: Add pagination
 
     interface TokenFamiliesList {
 
       // All configured token families of this instance.
       token_families: TokenFamilySummary[];
 
    }
 
   .. ts:def:: TokenFamilySummary
 
     interface TokenFamilySummary {
       // Identifier for the token family consisting of unreserved characters
       // according to RFC 3986.
       slug: string;
 
       // Human-readable name for the token family.
       name: string;
 
       // Human-readable description for the token family.
       // @since protocol **v23**.
       description: string;
 
       // Optional map from IETF BCP 47 language tags to localized descriptions.
       // @since protocol **v23**.
       description_i18n?: { [lang_tag: string]: string };
 
       // Start time of the token family's validity period.
       valid_after: Timestamp;
 
       // End time of the token family's validity period.
       valid_before: Timestamp;
 
       // Kind of the token family.
       kind: TokenFamilyKind;
    }
 
 
 .. http:get:: [/instances/$INSTANCES]/private/tokenfamilies/$TOKEN_FAMILY_SLUG
 
   This is used to get detailed information about a specific token family.
 
   **Required permission:** ``tokenfamilies-read``
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     The merchant backend has successfully returned the detailed information
     about a specific token family. Returns a `TokenFamilyDetails`.
 
   :http:statuscode:`404 Not found`:
     The merchant backend is unaware of the token family or instance.
 
   **Details:**
 
   The `TokenFamilyDetails` object describes a configured token family.
 
   .. ts:def:: TokenFamilyDetails
 
     interface TokenFamilyDetails {
 
       // Identifier for the token family consisting of unreserved characters
       // according to RFC 3986.
       slug: string;
 
       // Human-readable name for the token family.
       name: string;
 
       // Human-readable description for the token family.
       description: string;
 
       // Optional map from IETF BCP 47 language tags to localized descriptions.
       description_i18n?: { [lang_tag: string]: string };
 
       // Additional meta data, such as the ``trusted_domains``
       // or ``expected_domains``. Depends on the ``kind``.
       extra_data?: object;
 
       // Start time of the token family's validity period.
       // No token validities can start before this time
       // (but they could be sold before).
       valid_after: Timestamp;
 
       // End time of the token family's validity period.
       // No tokens will be accepted after this time.
       valid_before: Timestamp;
 
       // Validity duration of an issued token.
       duration: RelativeTime;
 
       // Rounding granularity for the start validity of keys.
       // The desired time is rounded down to a multiple of this
       // granularity and then the ``start_offset`` is added to
       // compute the actual start time of the token keys' validity.
       // The end is then computed by adding the ``duration``.
       validity_granularity: RelativeTime;
 
       // Offset in seconds to subtract from the start time rounded to ``validity_granularity``
       // to compute the actual start time for a key.
       start_offset: RelativeTime;
 
       // Kind of the token family.
       kind: TokenFamilyKind;
 
       // How many tokens have been issued for this family.
       issued: Integer;
 
       // How many tokens have been used for this family.
       used: Integer;
 
    }
 
 
 
 Deleting token families
 ^^^^^^^^^^^^^^^^^^^^^^^
 
 .. http:delete:: [/instances/$INSTANCES]/private/tokenfamilies/$TOKEN_FAMILY_SLUG
 
   This is used to delete a token family. Issued tokens of this family will not
   be spendable anymore.
 
   **Required permission:** ``tokenfamilies-write``
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The backend has successfully deleted the token family.
 
   :http:statuscode:`404 Not found`:
     The merchant backend is unaware of the token family or instance.
 
 
 -----------------------
 Donau Charity Instances
 -----------------------
 
 A merchant instance can link one or more **Donau charity instances**.
 Each link associates the instance’s own public key with a charity registered
 at some Donau service.  These links are managed under the private API.
 
 Permissions
 ^^^^^^^^^^^
 
 * ``donau-read``  — list linked charities.
 * ``donau-write`` — add or remove charity links.
 
 Listing charity instances
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 .. http:get:: [/instances/$INSTANCE]/private/donau
 
   Return all Donau charity instances currently linked to ``$INSTANCE``.
 
   **Required permission:** ``donau-read``
 
   **Response:**
 
   :http:statuscode:`200 OK`:
     Body is a :ts:type:`DonauInstancesResponse`.
   :http:statuscode:`401 Unauthorized`:
     Missing or invalid credentials.
   :http:statuscode:`404 Not found`:
     The merchant instance is unknown.
 
   **Details:**
 
   .. ts:def:: DonauInstancesResponse
 
     interface DonauInstancesResponse {
       // List of linked charity instances
       donau_instances: DonauInstance[];
     }
 
   .. ts:def:: DonauInstance
 
     interface DonauInstance {
       // Serial number identifying the record inside the backend
       donau_instance_serial: Integer;
 
       // Base URL of the Donau service
       donau_url: string;
 
       // Human-readable charity name
       charity_name: string;
 
       // EdDSA public key of the charity (binary)
       charity_pub_key: Bytes;
 
       // Charity identifier inside the Donau service
       charity_id: Integer;
 
       // Maximum donation amount per calendar year
       charity_max_per_year: Amount;
 
       // Cumulative receipts in the current year
       charity_receipts_to_date: Amount;
 
       // Calendar year the receipts refer to
       current_year: Integer;
 
       // Exchange-style ``/keys`` response published by Donau,
       // missing if not yet known to the merchant backend.
       donau_keys_json?: object;
     }
 
 Adding a charity instance
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 .. http:post:: [/instances/$INSTANCE]/private/donau
 
   Link a new Donau charity instance to ``$INSTANCE``.
   The backend fetches and validates the charity’s metadata from the given
   Donau service before persisting the link.
 
   **Required permission:** ``donau-write``
 
   **Request:**
 
   The body **must** be a :ts:type:`PostDonauRequest`.
 
   .. ts:def:: PostDonauRequest
 
     interface PostDonauRequest {
       // Base URL of the Donau service hosting the charity
       donau_url: string;
 
       // Numeric charity identifier inside the Donau service
       charity_id: Integer;
     }
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     The charity link was created successfully.
   :http:statuscode:`202 Accepted`:
     Operation requires MFA; a :ts:type:`ChallengeResponse` is returned.  @since **v21**
   :http:statuscode:`400 Bad request`:
     Malformed JSON or missing fields.
   :http:statuscode:`409 Conflict`:
     * The charity is already linked with different parameters, or
     * The charity’s public key does **not** match the merchant instance’s public key.
   :http:statuscode:`502 Bad gateway`:
     Communication with the Donau service failed.
 
 Deleting a charity instance
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 .. http:delete:: [/instances/$INSTANCE]/private/donau/$DONAU_SERIAL
 
   Unlink the Donau charity instance identified by ``$DONAU_SERIAL``.
 
   **Required permission:** ``donau-write``
 
   **Response:**
 
   :http:statuscode:`204 No content`:
     Charity link removed.
   :http:statuscode:`404 Not found`:
     No such charity link exists.
 
 
 
 ------------------
 The Contract Terms
 ------------------
 
 This section describes the overall structure of
 the contract terms that are the foundation for
 Taler payments.
 
 .. _contract-terms:
 
 The contract terms must have the following structure:
 
 .. ts:def:: ContractTerms
 
   type ContractTerms = (ContractTermsV1 | ContractTermsV0) & ContractTermsCommon;
 
 .. ts:def:: ContractTermsV1
 
   interface ContractTermsV1 {
     // Version 1 supports the ``choices`` array, see
     // https://docs.taler.net/design-documents/046-mumimo-contracts.html.
     // @since protocol **v21**
     version: 1;
 
     // List of contract choices that the customer can select from.
     // @since protocol **v21**
     choices: ContractChoice[];
 
     // Map of storing metadata and issue keys of
     // token families referenced in this contract.
     // @since protocol **v21**
     token_families: { [token_family_slug: string]: ContractTokenFamily };
   }
 
 .. ts:def:: ContractTermsV0
 
   interface ContractTermsV0 {
     // Defaults to version 0.
     version?: 0;
 
     // Total price for the transaction.
     // The exchange will subtract deposit fees from that amount
     // before transferring it to the merchant.
     amount: Amount;
 
     // Maximum total deposit fee accepted by the merchant for this contract.
     // Overrides defaults of the merchant instance.
     max_fee: Amount;
   }
 
 .. ts:def:: ContractTermsCommon
 
   interface ContractTermsCommon {
     // Human-readable description of the whole purchase.
     summary: string;
 
     // Map from IETF BCP 47 language tags to localized summaries.
     summary_i18n?: { [lang_tag: string]: string };
 
     // Unique, free-form identifier for the proposal.
     // Must be unique within a merchant instance.
     // For merchants that do not store proposals in their DB
     // before the customer paid for them, the ``order_id`` can be used
     // by the frontend to restore a proposal from the information
     // encoded in it (such as a short product identifier and timestamp).
     order_id: string;
 
     // URL where the same contract could be ordered again (if
     // available). Returned also at the public order endpoint
     // for people other than the actual buyer (hence public,
     // in case order IDs are guessable).
     public_reorder_url?: string;
 
     // URL that will show that the order was successful after
     // it has been paid for.  Optional, but either ``fulfillment_url``
     // or ``fulfillment_message`` must be specified in every
     // contract terms.
     //
     // If a non-unique fulfillment URL is used, a customer can only
     // buy the order once and will be redirected to a previous purchase
     // when trying to buy an order with the same fulfillment URL a second
     // time. This is useful for digital goods that a customer only needs
     // to buy once but should be able to repeatedly download.
     //
     // For orders where the customer is expected to be able to make
     // repeated purchases (for equivalent goods), the fulfillment URL
     // should be made unique for every order. The easiest way to do
     // this is to include a unique order ID in the fulfillment URL.
     //
     // When POSTing to the merchant, the placeholder text "${ORDER_ID}"
     // is be replaced with the actual order ID (useful if the
     // order ID is generated server-side and needs to be
     // in the URL). Note that this placeholder can only be used once.
     // Front-ends may use other means to generate a unique fulfillment URL.
     fulfillment_url?: string;
 
     // Message shown to the customer after paying for the order.
     // Either fulfillment_url or fulfillment_message must be specified.
     fulfillment_message?: string;
 
     // Map from IETF BCP 47 language tags to localized fulfillment
     // messages.
     fulfillment_message_i18n?: { [lang_tag: string]: string };
 
     // List of products that are part of the purchase (see `Product`).
     products: Product[];
 
     // Time when this contract was generated.
     timestamp: Timestamp;
 
     // After this deadline has passed, no refunds will be accepted.
     refund_deadline: Timestamp;
 
     // After this deadline, the merchant won't accept payments for the contract.
     pay_deadline: Timestamp;
 
     // Transfer deadline for the exchange.  Must be in the
     // deposit permissions of coins used to pay for this order.
     wire_transfer_deadline: Timestamp;
 
     // Merchant's public key used to sign this proposal; this information
     // is typically added by the backend. Note that this can be an ephemeral key.
     merchant_pub: EddsaPublicKey;
 
     // Base URL of the (public!) merchant backend API.
     // Must be an absolute URL that ends with a slash.
     merchant_base_url: string;
 
     // More info about the merchant, see below.
     merchant: Merchant;
 
     // The hash of the merchant instance's wire details.
     h_wire: HashCode;
 
     // Wire transfer method identifier for the wire method associated with ``h_wire``.
     // The wallet may only select exchanges via a matching auditor if the
     // exchange also supports this wire method.
     // The wire transfer fees must be added based on this wire transfer method.
     wire_method: string;
 
     // Exchanges that the merchant accepts even if it does not accept any auditors that audit them.
     exchanges: Exchange[];
 
     // Delivery location for (all!) products.
     delivery_location?: Location;
 
     // Time indicating when the order should be delivered.
     // May be overwritten by individual products.
     delivery_date?: Timestamp;
 
     // Nonce generated by the wallet and echoed by the merchant
     // in this field when the proposal is generated.
     nonce: string;
 
     // Specifies for how long the wallet should try to get an
     // automatic refund for the purchase. If this field is
     // present, the wallet should wait for a few seconds after
     // the purchase and then automatically attempt to obtain
     // a refund.  The wallet should probe until "delay"
     // after the payment was successful (i.e. via long polling
     // or via explicit requests with exponential back-off).
     //
     // In particular, if the wallet is offline
     // at that time, it MUST repeat the request until it gets
     // one response from the merchant after the delay has expired.
     // If the refund is granted, the wallet MUST automatically
     // recover the payment.  This is used in case a merchant
     // knows that it might be unable to satisfy the contract and
     // desires for the wallet to attempt to get the refund without any
     // customer interaction.  Note that it is NOT an error if the
     // merchant does not grant a refund.
     auto_refund?: RelativeTime;
 
     // Extra data that is only interpreted by the merchant frontend.
     // Useful when the merchant needs to store extra information on a
     // contract without storing it separately in their database.
     // Must really be an Object (not a string, integer, float or array).
     extra?: Object;
 
     // Minimum age the buyer must have (in years). Default is 0.
     // This value is at least as large as the maximum over all
     // mimimum age requirements of the products in this contract.
     // It might also be set independent of any product, due to
     // legal requirements.
     minimum_age?: Integer;
 
   }
 
 .. ts:def:: ContractChoice
 
   interface ContractChoice {
     // Price to be paid for this choice. Could be 0.
     // The price is in addition to other instruments,
     // such as rations and tokens.
     // The exchange will subtract deposit fees from that amount
     // before transferring it to the merchant.
     amount: Amount;
 
     // Human readable description of the semantics of the choice
     // within the contract to be shown to the user at payment.
     description?: string;
 
     // Map from IETF 47 language tags to localized descriptions.
     description_i18n?: { [lang_tag: string]: string };
 
     // List of inputs the wallet must provision (all of them) to
     // satisfy the conditions for the contract.
     inputs: ContractInput[];
 
     // List of outputs the merchant promises to yield (all of them)
     // once the contract is paid.
     outputs: ContractOutput[];
 
     // Maximum total deposit fee accepted by the merchant for this contract.
     max_fee: Amount;
   }
 
 .. ts:def:: ContractInput
 
   // For now, only tokens are supported as inputs.
   type ContractInput = ContractInputToken;
 
 .. ts:def:: ContractInputToken
 
   interface ContractInputToken {
     type: "token";
 
     // Slug of the token family in the
     // ``token_families`` map on the order.
     token_family_slug: string;
 
     // Number of tokens of this type required.
     // Defaults to one if the field is not provided.
     count?: Integer;
   };
 
 .. ts:def:: ContractOutput
 
   // For now, only tokens are supported as outputs.
   type ContractOutput = ContractOutputToken | ContractOutputTaxReceipt;
 
 .. ts:def:: ContractOutputToken
 
   interface ContractOutputToken {
     type: "token";
 
     // Slug of the token family in the
     // 'token_families' map on the top-level.
     token_family_slug: string;
 
     // Number of tokens to be issued.
     // Defaults to one if the field is not provided.
     count?: Integer;
 
     // Index of the public key for this output token
     // in the `ContractTokenFamily` ``keys`` array.
     key_index: Integer;
 
   }
 
 .. ts:def:: ContractOutputTaxReceipt
 
   interface ContractOutputTaxReceipt {
 
     // Tax receipt output.
     type: "tax-receipt";
 
     // Array of base URLs of donation authorities that can be
     // used to issue the tax receipts. The client must select one.
     donau_urls: string[];
 
     // Total amount that will be on the tax receipt.
     amount: Amount;
 
   }
 
 .. ts:def:: ContractTokenFamily
 
   interface ContractTokenFamily {
     // Human-readable name of the token family.
     name: string;
 
     // Human-readable description of the semantics of
     // this token family (for display).
     description: string;
 
     // Map from IETF BCP 47 language tags to localized descriptions.
     description_i18n?: { [lang_tag: string]: string };
 
     // Public keys used to validate tokens issued by this token family.
     keys: TokenIssuePublicKey[];
 
     // Kind-specific information of the token
     details: ContractTokenDetails;
 
     // Must a wallet understand this token type to
     // process contracts that use or issue it?
     critical: boolean;
   };
 
 .. ts:def:: TokenIssuePublicKey
 
   type TokenIssuePublicKey =
     | TokenIssueRsaPublicKey
     | TokenIssueCsPublicKey;
 
 .. ts:def:: TokenIssueRsaPublicKey
 
   interface TokenIssueRsaPublicKey {
     cipher: "RSA";
 
     // RSA public key.
     rsa_pub: RsaPublicKey;
 
     // Start time of this key's signatures validity period.
     signature_validity_start: Timestamp;
 
     // End time of this key's signatures validity period.
     signature_validity_end: Timestamp;
 
   }
 
 .. ts:def:: TokenIssueCsPublicKey
 
   interface TokenIssueCsPublicKey {
     cipher: "CS";
 
     // CS public key.
     cs_pub: Cs25519Point;
 
     // Start time of this key's signatures validity period.
     signature_validity_start: Timestamp;
 
     // End time of this key's signatures validity period.
     signature_validity_end: Timestamp;
 
   }
 
 .. ts:def:: ContractTokenDetails
 
   type ContractTokenDetails =
     | ContractSubscriptionTokenDetails
     | ContractDiscountTokenDetails;
 
 .. ts:def:: ContractSubscriptionTokenDetails
 
   interface ContractSubscriptionTokenDetails {
     class: "subscription";
 
     // Array of domain names where this subscription
     // can be safely used (e.g. the issuer warrants that
     // these sites will re-issue tokens of this type
     // if the respective contract says so).  May contain
     // "*" for any domain or subdomain.
     trusted_domains: string[];
   };
 
 .. ts:def:: ContractDiscountTokenDetails
 
   interface ContractDiscountTokenDetails {
     class: "discount";
 
     // Array of domain names where this discount token
     // is intended to be used.  May contain "*" for any
     // domain or subdomain.  Users should be warned about
     // sites proposing to consume discount tokens of this
     // type that are not in this list that the merchant
     // is accepting a coupon from a competitor and thus
     // may be attaching different semantics (like get 20%
     // discount for my competitors 30% discount token).
     expected_domains: string[];
   };
 
 
 The wallet must select an exchange that either the merchant accepts directly by
 listing it in the exchanges array, or for which the merchant accepts an auditor
 that audits that exchange by listing it in the auditors array.
 
 The `Product` object describes the product being purchased from the merchant.
 It has the following structure:
 
 .. ts:def:: Product
 
   interface Product {
 
     // Merchant-internal identifier for the product.
     product_id?: string;
 
     // Name of the product.
     // Since API version **v20**.  Optional only for
     // backwards-compatibility, should be considered mandatory
     // moving forward!
     product_name?: string;
 
     // Human-readable product description.
     description: string;
 
     // Map from IETF BCP 47 language tags to localized descriptions.
     description_i18n?: { [lang_tag: string]: string };
 
     // Legacy integer portion of the quantity to deliver defaults to 1 if not specified.
     quantity?: Integer;
 
     // Preferred quantity string using "<integer>[.<fraction>]" syntax with up to six fractional digits.
     unit_quantity?: string;
 
     // Unit in which the product is measured (liters, kilograms, packages, etc.).
     unit?: string;
 
     // The price of the product; this is the total price for ``quantity`` times ``unit`` of this product.
     price?: Amount;
 
     // An optional base64-encoded product image.
     image?: ImageDataUrl;
 
     // A list of taxes paid by the merchant for this product. Can be empty.
     taxes?: Tax[];
 
     // Time indicating when this product should be delivered.
     delivery_date?: Timestamp;
   }
 
 .. ts:def:: Tax
 
   interface Tax {
     // The name of the tax.
     name: string;
 
     // Amount paid in tax.
     tax: Amount;
   }
 
 .. ts:def:: Merchant
 
   interface Merchant {
     // The merchant's legal name of business.
     name: string;
 
     // Email address for contacting the merchant.
     email?: string;
 
     // Label for a location with the business address of the merchant.
     website?: string;
 
     // An optional base64-encoded product image.
     logo?: ImageDataUrl;
 
     // Label for a location with the business address of the merchant.
     address?: Location;
 
     // Label for a location that denotes the jurisdiction for disputes.
     // Some of the typical fields for a location (such as a street address) may be absent.
     jurisdiction?: Location;
   }
 
 
 .. ts:def:: Location
 
   // Delivery location, loosely modeled as a subset of
   // ISO20022's PostalAddress25.
   interface Location {
     // Nation with its own government.
     country?: string;
 
     // Identifies a subdivision of a country such as state, region, county.
     country_subdivision?: string;
 
     // Identifies a subdivision within a country sub-division.
     district?: string;
 
     // Name of a built-up area, with defined boundaries, and a local government.
     town?: string;
 
     // Specific location name within the town.
     town_location?: string;
 
     // Identifier consisting of a group of letters and/or numbers that
     // is added to a postal address to assist the sorting of mail.
     post_code?: string;
 
     // Name of a street or thoroughfare.
     street?: string;
 
     // Name of the building or house.
     building_name?: string;
 
     // Number that identifies the position of a building on a street.
     building_number?: string;
 
     // Free-form address lines, should not exceed 7 elements.
     address_lines?: string[];
   }
 
 .. ts:def:: Auditor
 
   interface Auditor {
     // Official name.
     name: string;
 
     // Auditor's public key.
     auditor_pub: EddsaPublicKey;
 
     // Base URL of the auditor.
     url: string;
   }
 
 .. ts:def:: Exchange
 
   interface Exchange {
     // The exchange's base URL.
     url: string;
 
     // How much would the merchant like to use this exchange.
     // The wallet should use a suitable exchange with high
     // priority. The following priority values are used, but
     // it should be noted that they are NOT in any way normative.
     //
     // 0: likely it will not work (recently seen with account
     //    restriction that would be bad for this merchant)
     // 512: merchant does not know, might be down (merchant
     //    did not yet get /wire response).
     // 1024: good choice (recently confirmed working)
     priority: Integer;
 
     // Master public key of the exchange.
     master_pub: EddsaPublicKey;
 
     // Maximum amount that the merchant could be paid
     // using this exchange (due to legal limits).
     // New in protocol **v17**.
     // Optional, no limit if missing.
     max_contribution?: Amount;
   }
 
 In addition to the fields described above,
 each object (from ``ContractTerms`` down)
 can mark certain fields as "forgettable" by listing the names of those fields
 in a special peer field ``_forgettable``.
 (See :ref:`Private order data cleanup <private-order-data-cleanup>`.)