> ## Documentation Index
> Fetch the complete documentation index at: https://docs.atum.xyz/llms.txt
> Use this file to discover all available pages before exploring further.

# API Reference

> Reference for Atum's hosted REST APIs — Payment Gateway and x402 Facilitator — and the request_id, authentication, and error conventions those APIs share.

This reference documents Atum's hosted REST APIs. See each endpoint page for full request and response shapes.

## Atum APIs

| API                                                            | What it does                                                                                                                                                             |
| -------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| [Payment Gateway](/api-reference/payment-gateway/introduction) | The entry point for most integrations: submit signed payments, poll status, resolve by `request_id`, and open quote-request batches. Also serves x402 corridor defaults. |
| [x402 Facilitator](/api-reference/x402/introduction)           | `/verify`, `/settle`, and `/supported`, served by the Payment Gateway under the `/x402/v1` prefix.                                                                       |

## Authentication

There is no API key: a payment authorizes itself through the `sender_auth` signature it carries, and read endpoints (`/status`, `/resolve`, `/timeline`) need no credentials.

## Idempotency and error handling

Cross-cutting behavior for these APIs:

| Topic                                     | Covers                                                                                           |
| ----------------------------------------- | ------------------------------------------------------------------------------------------------ |
| [Idempotency](/api-reference/idempotency) | Retrying a write safely by reusing a `request_id`.                                               |
| [Error codes](/errors)                    | The `IDEMPOTENCY_TERMS_MISMATCH`, `INVALID_REQUEST_ID`, and other codes an HTTP error can carry. |
| [Decline reasons](/decline-reasons)       | Why a settler said no inside a `200` response.                                                   |

## Base URLs

See [base URLs](/get-started/reference/endpoints) for testnet and mainnet.

## Getting started

Build and sign a request with the [SDK or CLI](/get-started/start-building/build-with-the-sdk), then submit it to [`POST /v1/payments`](/api-reference/payment-gateway/submit-payment).