# Applies the vendor credit to the given vendor bills.

`POST /accounting/vendor-credits/{id}/apply`

Group: Accounting › Vendor Credits · Operation ID: `applyVendorCredit`

Applies the vendor credit to one or more vendor bills, reducing what each bill still owes. Each application names a bill and an amount, and the amount cannot exceed the bill's open amount or the credit's remaining balance. Applying is reversible with POST accounting/vendor-credits/:id/unapply. A bill with applied credits cannot be reversed until they are detached.

[Open in the interactive reference](https://docs.api.lensing.ai/?op=applyVendorCredit)

## 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 vendor credit to apply. |

## Request body

Required, `application/json`: applyVendorCreditInput.

| Field | Type | Required | Description |
| --- | --- | --- | --- |
| `applications` | array of object | yes | The bills this credit is applied to, and how much goes to each. At least one is required. |
| `applications[].vendorBillId` | string | yes | The vendor bill the credit is applied to. See id on GET accounting/vendor-bills/:id. |
| `applications[].amount` | string (decimal) | yes | The amount applied to this bill, as a decimal in the bill's currency. It cannot exceed the bill's open amount or the credit's remaining balance. |
| `applications[].appliedDate` | string (date) | no | The date the application is recorded on. Use format YYYY-MM-DD. It must be on or after both the bill date and the credit date. Defaults to today in the owning entity's time zone. |

Example:

```json
{
  "applications": [
    {
      "vendorBillId": "9b2d5e10-4c78-4a36-8f51-6e0a3c7b2d95",
      "amount": "300.00",
      "appliedDate": "2026-08-20"
    }
  ]
}
```

## Response

`200` Success

Under `data` (applyVendorCreditOutput):

| Field | Type | Required | Description |
| --- | --- | --- | --- |
| `appliedCount` | number | yes | The number of applications recorded. Read the credit with GET accounting/vendor-credits/:id for its remaining balance. |

## 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 |
| `REFERENCE_NOT_FOUND` | 400 |
| `NO_APPLICATIONS` | 400 |
| `APPLICATION_REJECTED` | 400 |
| `IDEMPOTENCY_KEY_CONFLICT` | 409 |
| `IDEMPOTENCY_PAYLOAD_MISMATCH` | 422 |

## Statuses

- `400` — Invalid request or business failure. Codes: NOT_FOUND, REFERENCE_NOT_FOUND, NO_APPLICATIONS, APPLICATION_REJECTED
- `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