# Reference

## What is x402?

[x402](https://x402.org) is an open standard for internet-native payments over HTTP. It brings back the original intent of the HTTP `402 Payment Required` status code, enabling any HTTP resource to require a micro-payment before delivering its response.

The protocol is designed to be stateless and works for both traditional applications and autonomous AI agents. The payment flow follows six steps:

1. The client requests a paid resource.
2. The server responds with `402 Payment Required` and a `PaymentRequirements` object describing the accepted network, scheme, asset, and amount.
3. The client builds a signed `PaymentPayload` and replays the request with a `PAYMENT-SIGNATURE` header.
4. The server forwards the payload to a **facilitator** for verification and settlement.
5. The facilitator validates the payload and submits the payment on-chain.
6. The server delivers the protected resource upon confirmation.

## What is a facilitator?

A facilitator is a service that handles the verification and on-chain settlement of x402 payments on behalf of resource servers. It operates as an independent layer between clients, resource servers, and blockchain networks.

The facilitator's three core responsibilities are:

* **Verification** — Confirms that a client's signed payment payload satisfies the server's declared payment requirements without yet submitting anything on-chain.
* **Settlement** — Validates the payload and then submits the payment transaction to the blockchain, monitoring it until confirmation.
* **Abstraction** — Allows resource servers to accept blockchain payments without maintaining direct node connectivity or building their own verification logic.

The facilitator does not hold funds or act as a custodian. It only executes on-chain transactions based on signed payment authorizations provided by clients.

## CSPR.cloud x402 Facilitator

CSPR.cloud provides an x402 facilitator for the Casper Network. It supports the `exact` payment scheme using [CEP-18](https://github.com/casper-ecosystem/cep18) tokens authorized via [EIP-712](https://github.com/casper-ecosystem/casper-eip-712) typed-data signatures.

### Endpoints

| URL                                   | Network             |
| ------------------------------------- | ------------------- |
| <https://x402-facilitator.cspr.cloud> | Mainnet and Testnet |

All endpoints require authorization. Learn how to obtain an access token [here](/documentation/overview/authorization.md).

### Supported networks and schemes

The CSPR.cloud facilitator supports the `exact` scheme on Casper networks:

| Network identifier   | Description    |
| -------------------- | -------------- |
| `casper:casper`      | Casper Mainnet |
| `casper:casper-test` | Casper Testnet |

Network identifiers follow the [CAIP-2](https://github.com/ChainAgnostic/namespaces/blob/main/casper/caip2.md) format.

### API endpoints

The facilitator exposes three endpoints:

| Endpoint                                         | Method | Description                                                      |
| ------------------------------------------------ | ------ | ---------------------------------------------------------------- |
| [/supported](/x402-facilitator-api/supported.md) | GET    | Returns supported payment schemes and networks                   |
| [/verify](/x402-facilitator-api/verify.md)       | POST   | Validates a payment payload without submitting it on-chain       |
| [/settle](/x402-facilitator-api/settle.md)       | POST   | Validates a payment payload and settles it on the Casper Network |

### Examples

The [github.com/make-software/casper-x402](https://github.com/make-software/casper-x402) repository contains end-to-end examples to build a complete x402 payment flow.


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