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

# Facilitator

> x402 verify and settle endpoints, chain metadata, and payment intents.

The facilitator endpoints expose the x402 pieces directly. The payment intent endpoints expose the Compose reserve-settle-abort flow used by Compose Keys and metered calls.

## x402 endpoints

| Method | Path                              | Purpose                                                                                       |
| ------ | --------------------------------- | --------------------------------------------------------------------------------------------- |
| `GET`  | `/api/x402/facilitator/supported` | Lists supported x402 versions, networks, and schemes.                                         |
| `GET`  | `/api/x402/facilitator/chains`    | Lists configured chains, CAIP-2 network IDs, USDC addresses, explorers, and default chain ID. |
| `POST` | `/api/x402/facilitator/verify`    | Verifies a payment payload against payment requirements.                                      |
| `POST` | `/api/x402/facilitator/settle`    | Settles a payment payload.                                                                    |

`verify` and `settle` accept x402-shaped `paymentPayload` and `paymentRequirements` objects.

## Payment-required challenge

Raw x402 calls start with a normal request. If no valid payment is present, Compose responds with:

```http theme={null}
HTTP/1.1 402 Payment Required
PAYMENT-REQUIRED: <base64-json>
Content-Type: application/json
```

The client signs the requirement and retries with:

```http theme={null}
PAYMENT-SIGNATURE: <signed-payment-payload>
```

## Payment intents

| Method | Path                        | Purpose                                                       |
| ------ | --------------------------- | ------------------------------------------------------------- |
| `POST` | `/api/payments/prepare`     | Authorizes an exact amount, a metered quote, or a budget cap. |
| `POST` | `/api/payments/settle`      | Settles an intent with a final amount or metered usage.       |
| `POST` | `/api/payments/abort`       | Releases a prepared intent when work fails before settlement. |
| `POST` | `/api/payments/meter/model` | Prices model usage using catalog pricing.                     |

```mermaid theme={null}
stateDiagram-v2
  [*] --> authorized
  authorized --> settling
  authorized --> aborted
  settling --> settled
  settling --> failed
```

## Quote model usage

```http theme={null}
POST /api/payments/meter/model
Content-Type: application/json
```

```json theme={null}
{
  "modelId": "gpt-5.5",
  "provider": "azure",
  "modality": "text",
  "usage": {
    "promptTokens": 1000,
    "completionTokens": 250,
    "totalTokens": 1250
  }
}
```

The response contains the resolved model, meter subject, line items, provider amount, platform fee, and final USDC atomic amount.

## Receipt headers

| Header                | Meaning                                                                |
| --------------------- | ---------------------------------------------------------------------- |
| `PAYMENT-RESPONSE`    | Encoded x402 settlement response.                                      |
| `X-Transaction-Hash`  | Settlement transaction hash when available.                            |
| `X-Receipt`           | Compose receipt with amount, network, line items, and settlement time. |
| `x-payment-intent-id` | Prepared payment intent ID.                                            |

## Related

* [x402 introduction](/x402/introduction)
* [Compose Keys](/x402/compose-key)
* [Inference metering](/inference/metering)