# X402 Protocol

AESC integrates the X402 payment protocol, which implements on-chain micropayments based on the HTTP 402 status code. It is particularly suited for the AI Agent economy and API monetization.

## Architecture

```
Client (User/AI Agent)
    |
    |-- 1. HTTP Request ----------------> Protected API Service
    |                                          |
    |                                    2. Returns 402 + Payment Requirements
    |                                          |
    |-- 3. EIP-712 Signed Payment ----> x402-relayer (Go Service)
    |                                          |
    |                                    4. Verify Signature + On-chain Settlement
    |                                          |
    <-- 5. API Response -----------------------+
```

## Core Components

| Component               | Description                                                                            |
| ----------------------- | -------------------------------------------------------------------------------------- |
| **x402-relayer**        | A standalone Go service responsible for signature verification and on-chain settlement |
| **Facilitator**         | Local verification/settlement module (EIP-712 signature verification)                  |
| **HTTP 402 Middleware** | Intercepts requests and returns payment requirements                                   |

## Supported Payment Tokens

<table><thead><tr><th width="98.41015625">Token</th><th width="267.9375">Contract Address (Testnet)</th><th>Contract Address (Mainnet)</th></tr></thead><tbody><tr><td>USDT</td><td>0x2F3a429D90e4aD9A4984EA98Ed05D3f6D69dFf37</td><td>TBD</td></tr><tr><td>USDC</td><td>TBD</td><td>TBD</td></tr></tbody></table>

## Detailed Payment Flow

1. **Client Request**: The client sends an HTTP request to an X402-protected API
2. **402 Response**: The server returns an HTTP 402 status code with a payment descriptor (PaymentRequired header), containing:
   * Payment amount
   * Token type (USDT/USDC)
   * Recipient address
   * Expiration time
3. **Offline Signing**: The client uses EIP-712 typed data signing to authorize the payment (`transferWithAuthorization`, EIP-3009)
4. **Verification and Settlement**: The x402-relayer verifies the signature validity and executes the token transfer on-chain
5. **Response Return**: After successful settlement, the original API response is returned to the client

## Features

* **No Gas Token Required**: Users pay with USDT/USDC without needing to hold AEX
* **EIP-712 Offline Signing**: Users do not need to authorize online, reducing interaction friction
* **EIP-3009 Compatible**: Uses `transferWithAuthorization` for authorized transfers
* **Independent Deployment**: The x402-relayer runs as a standalone service, not embedded in chain nodes

***

> **Developer Note**: 1 AEX = 10^6 wei precision (6 decimal places).


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