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The x402 protocol enables seamless machine-to-machine payments using HTTP status codes. It extends HTTP with a payment flow based on the 402 Payment Required status code.

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How It Works

The payment flow is fully automated by the MCP server:
1

Agent calls create_order

The AI agent calls create_order or renew_instance with product details.
2

Server returns HTTP 402

The first request returns HTTP 402 with a payment-required header containing payment requirements (amount, recipient, asset, network).
3

Client signs payment

The MCP client signs a USDC transfer authorization using EIP-3009 (TransferWithAuthorization) — no on-chain transaction needed at this point.
4

Retry with signature

The request is retried with the payment signature in the payment-signature header.
5

Server verifies and settles

The server verifies the signature, settles the USDC transfer on-chain (Base network), and creates the order.
6

Order returned

The completed order is returned to the agent with instance details.

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EIP-3009: TransferWithAuthorization

The payment uses EIP-3009 which allows gasless USDC transfers via signed authorizations:
  • No gas needed — The wallet signs a typed data message (EIP-712), not a transaction
  • Server submits — The server submits the authorization on-chain
  • USDC only — Only works with USDC on Base network
  • Time-bounded — Authorization has validAfter and validBefore timestamps
  • Nonce-protected — Each authorization uses a unique random nonce

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Payment Payload Structure

The signed payment is encoded as a base64 JSON payload: