Protocol

MicroAI Paygate currently implements a custom x402-style protocol. It uses HTTP 402 Payment Required, EIP-712 typed data, custom X-402-* retry headers, and gateway-signed receipts.

It is not official x402-compatible yet because it does not use the official header contract or facilitator-backed settlement path.

Flow

1. Client sends an unsigned request to the gateway.
2. Gateway returns 402 Payment Required with a paymentContext.
3. Client signs the payment context with EIP-712.
4. Client retries with X-402-Signature, X-402-Nonce, and X-402-Timestamp.
5. Gateway sends the signed payload to the Rust verifier.
6. Verifier recovers the wallet, checks chain ID, timestamp, and nonce.
7. Gateway calls the configured AI provider.
8. Gateway signs a receipt over the request and response hashes.
9. Client decodes and verifies the receipt.

EIP-712 Domain

const domain = {
  name: "MicroAI Paygate",
  version: "1",
  chainId: paymentContext.chainId,
  verifyingContract: ethers.ZeroAddress,
};

Payment Type

const types = {
  Payment: [
    { name: "recipient", type: "address" },
    { name: "token", type: "string" },
    { name: "amount", type: "string" },
    { name: "nonce", type: "string" },
    { name: "timestamp", type: "uint256" },
  ],
};

Payment Context Fields

• recipient: recipient wallet address.
• token: display token symbol, currently USDC.
• amount: requested payment amount as a string.
• nonce: one-time replay protection value.
• chainId: EIP-712 chain ID.
• timestamp: signature freshness timestamp.

Receipt Fields

Receipts include:

• payment payer, recipient, amount, token, chain ID, and nonce.
• service endpoint.
• request_hash.
• response_hash.
• gateway signature.
• gateway server public key.

Receipt verification must use a trusted gateway public key distributed out of band. A client must not treat a public key embedded in the receipt as the trust anchor by itself.