Reverses a payment's application to one or more invoices.

POST /accounting/payments/{id}/unapply

Group: Accounting › Payments · Operation ID: unapplyPayment

Parameters

Name	In	Type	Required	Description
`Api-Version`	header	`"v1"`	yes	The API version this request targets, named by its public identifier. Required on every request; omitting it, or naming a version this company does not have, is answered with 400. This document describes version `v1`.
`Idempotency-Key`	header	string	no	An opaque caller-chosen string (1-255 characters) that makes this request safe to retry. Repeating the same key with an identical request body replays the original response instead of re-executing - but only once that original request succeeded; a failed attempt re-executes on retry. Repeating the key with a different body is answered with 422. A key still in flight is answered with 409 - as is a key whose original request was interrupted before it finished, for a few minutes afterwards, until that attempt is presumed dead. A completed response stays replayable for 24 hours. The key is scoped to the caller, not to the action: reusing it for a different action is answered with 409 or 422 rather than treated independently. On read actions this header is ignored. On write actions that cannot offer the guarantee it is answered with `400 IDEMPOTENCY_NOT_SUPPORTED` rather than silently ignored.
`id`	path	string	yes	The unique identifier for the payment to unapply.

Request body

Required, application/json: unapplyPaymentInput.

Field	Type	Required	Description
`invoices`	array of object	yes	The per-invoice amounts to unapply from the payment.
`invoices[].invoiceId`	string	yes	The invoice to unapply the payment from. See id on GET accounting/invoices/:id.
`invoices[].amount`	string (decimal)	yes	The amount to unapply from this invoice, in the payment currency. Must be greater than 0.
`invoices[].unappliedDate`	string (date)	yes	The date the reversal is recognized. Use format YYYY-MM-DD.
`invoices[].earlyPaymentDiscount`	string (decimal)	no	The early-payment discount to reverse for this invoice, in the payment currency.
`invoices[].smallBalanceWriteOffAmount`	string (decimal)	no	The small-balance write-off amount to reverse for this invoice, in the payment currency.

Example:

{
  "invoices": [
    {
      "invoiceId": "3fa85f64-5717-4562-b3fc-2c963f66afa6",
      "amount": "19.99",
      "unappliedDate": "2026-01-15",
      "earlyPaymentDiscount": "19.99",
      "smallBalanceWriteOffAmount": "19.99"
    }
  ]
}

Response

200 Success

Response headers

Idempotency-Replayed — Present and true only when this response replays a previously stored one for the same Idempotency-Key, rather than reflecting a live execution. Absent on a live response - never sent as false.

Errors

Code	Status
`NOT_FOUND`	400
`INVALID_AMOUNT`	400
`INVOICE_NOT_FOUND`	400
`LOCKED_ACCOUNTING_PERIOD`	400
`IDEMPOTENCY_KEY_CONFLICT`	409
`IDEMPOTENCY_PAYLOAD_MISMATCH`	422

Statuses

400 — Invalid request or business failure. Codes: NOT_FOUND, INVALID_AMOUNT, INVOICE_NOT_FOUND, LOCKED_ACCOUNTING_PERIOD
401 — Missing or invalid access token
403 — Not authorized
404 — Not found
409 — The Idempotency-Key is still being processed by another request.
422 — The Idempotency-Key was already used with a different request payload.
429 — Too many requests
500 — Internal server error