X402 Payment Protocol

X402 Payment Protocol

Agentis implements the X402 HTTP payment protocol, the emerging standard for AI agent payments.

Overview

The X402 protocol enables:

• Standardized Payments - Consistent payment flow across all APIs
• Agent Compatibility - AI agents can automatically handle payments
• Micro-transactions - Support for very small payments per API call
• Global Accessibility - No KYC or traditional banking required

Protocol Flow

1. Initial Request - Client makes request to API endpoint
2. Payment Required - Server responds with 402 status and payment details
3. Payment Processing - Client processes payment using specified method
4. Authenticated Request - Client retries request with payment proof
5. Response Delivery - Server validates payment and returns data

Response Format

When payment is required, APIs return a 402 status with payment details:

HTTP/1.1 402 Payment Required
Content-Type: application/json

{
  "x402Version": 1,
  "error": "Payment required",
  "accepts": [{
    "scheme": "eip712",
    "network": "base",
    "maxAmountRequired": "1000000",
    "resource": "/api/protected",
    "payTo": "0x742d35Cc6634C0532925a3b8D71E432BD78FE7",
    "asset": "USDC"
  }]
}

Payment Schemes

EIP-712 Signatures

The primary payment method uses EIP-712 typed signatures:

{
  "scheme": "eip712",
  "network": "base",
  "maxAmountRequired": "1000000",
  "payTo": "0x742d35Cc6634C0532925a3b8D71E432BD78FE7",
  "asset": "USDC"
}

Header Format (Legacy)

Some APIs may use the legacy header-based format:

HTTP/1.1 402 Payment Required
X-Payment-Requirements: {"amount":"0.01","token":"USDC","recipient":"0x...","chain":1}

Implementation

When implementing X402 in your API:

1. Detect payment requirement - Check if user has valid payment session
2. Return 402 response - Include payment details in response body
3. Validate payment proof - Verify payment signature on retry
4. Process request - Handle the original request after payment validation

Benefits for AI Agents

• Automatic discovery - Agents can detect payment requirements
• Standardized flow - Consistent payment process across services
• Micro-payment support - Enable small, frequent payments
• No human intervention - Fully autonomous payment processing