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	11	Vendor CRUD, bank accounts, data requests
Bills	12	Bill CRUD, approval workflow, OCR upload
Vendor Payments	4	Payment initiation, cancellation, retry
Webhooks	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:

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

Error Format

{
  "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")