# Reverses the vendor bill.

`POST /accounting/vendor-bills/{id}/reverse`

Group: Accounting › Vendor Bills · Operation ID: `reverseVendorBill`

Reverses the vendor bill, creating a reversing journal entry dated reversalDate. Reverse differs from void in when the ledger effect lands: a void backs the bill out as of its own posting period, and a reversal lets you choose the date, which a closed period requires. Only an approved bill that is neither voided nor already reversed may be reversed. A bill with applied vendor credits gives BILL_HAS_APPLIED_CREDITS, so unapply them first. A bill with any payment gives BILL_PAID. Remitted withholding gives WITHHOLDING_REMITTED. A reversal date no accounting period covers gives NO_ACCOUNTING_PERIOD, and a closed or locked one gives POSTING_PERIOD_CLOSED. The response is empty.

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

## 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 bill to reverse. |

## Request body

Required, `application/json`: reverseVendorBillInput.

| Field | Type | Required | Description |
| --- | --- | --- | --- |
| `reversalDate` | string (date) | yes | The date the reversing journal entry is posted on. Use format YYYY-MM-DD. Choose a date whose period is open. |

Example:

```json
{
  "reversalDate": "2026-09-30"
}
```

## 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 |
| `BILL_NOT_APPROVED` | 400 |
| `BILL_ALREADY_VOIDED` | 400 |
| `BILL_PAID` | 400 |
| `WITHHOLDING_REMITTED` | 400 |
| `BILL_ALREADY_REVERSED` | 400 |
| `BILL_HAS_APPLIED_CREDITS` | 400 |
| `NO_ACCOUNTING_PERIOD` | 400 |
| `POSTING_PERIOD_CLOSED` | 400 |
| `JOURNAL_ENTRY_VOIDED` | 400 |
| `IDEMPOTENCY_KEY_CONFLICT` | 409 |
| `IDEMPOTENCY_PAYLOAD_MISMATCH` | 422 |

## Statuses

- `400` — Invalid request or business failure. Codes: NOT_FOUND, BILL_NOT_APPROVED, BILL_ALREADY_VOIDED, BILL_PAID, WITHHOLDING_REMITTED, BILL_ALREADY_REVERSED, BILL_HAS_APPLIED_CREDITS, NO_ACCOUNTING_PERIOD, POSTING_PERIOD_CLOSED, JOURNAL_ENTRY_VOIDED
- `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