> For the complete documentation index, see [llms.txt](https://help.alternativepayments.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.alternativepayments.io/getting-started/accounts-payable-api.md).

# Accounts Payable API Reference

API Version: v1.2.0

The Accounts Payable API extends the existing Alternative Payments Partner API with endpoints for managing vendors, bills, and outbound payments. Partners can programmatically create vendors, submit bills for approval, initiate payments to vendors, and track the full bill-to-payment lifecycle.

All endpoints follow the same conventions as the existing Accounts Receivable API: OAuth2 client credentials authentication, cursor-based pagination, snake\_case JSON, idempotency keys on mutating operations, and standard error responses.

## Base URL

```
https://public-api.alternativepayments.io
```

## Authentication

Same OAuth2 client credentials flow as the AR API. Authenticate with your API key and secret to `/oauth/token`, then use the returned Bearer token for all requests.

## Resource Groups

| Group                                                                       | Endpoints     | Description                                       |
| --------------------------------------------------------------------------- | ------------- | ------------------------------------------------- |
| [Vendors](/getting-started/accounts-payable-api/vendors.md)                 | 11            | Vendor CRUD, bank accounts, data requests         |
| [Bills](/getting-started/accounts-payable-api/bills.md)                     | 12            | Bill CRUD, approval workflow, OCR upload          |
| [Vendor Payments](/getting-started/accounts-payable-api/vendor-payments.md) | 4             | Payment initiation, cancellation, retry           |
| [Webhooks](/getting-started/accounts-payable-api/webhooks.md)               | 14 new topics | Event notifications for all Acc Payable resources |

## Pagination

All list endpoints use cursor-based pagination:

| Parameter | Type    | Description                  |
| --------- | ------- | ---------------------------- |
| `limit`   | integer | Items per page (default 100) |
| `after`   | string  | Forward pagination cursor    |
| `before`  | string  | Backward pagination cursor   |

Response includes:

```json
{
  "data": [...],
  "has_next_page": true,
  "has_previous_page": false,
  "start_cursor": "abc123",
  "end_cursor": "xyz789"
}
```

## Error Format

```json
{
  "code": "BILL_NOT_FOUND",
  "message": "Bill with ID xyz not found",
  "validation_errors": {}
}
```

## Idempotency

Include an `Idempotency-Key` header on POST requests that create resources or initiate payments. The key must be a UUID. Duplicate requests with the same key return the original response.

## Naming Conventions

* All JSON fields use `snake_case`
* All IDs are UUID strings
* All dates use RFC3339 format
* All monetary amounts are decimal strings (e.g., `"1500.00"`)


---

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