x402 Micropayments

What is x402?

x402 is a machine-to-machine payment protocol built around HTTP 402 Payment Required. It enables AI agents to automatically pay for API access without human intervention. AgentWallex implements x402 v2 with EIP-3009 authorization payloads.

x402 v2 Headers

The protocol uses three HTTP headers:

Header	Direction	Purpose
`PAYMENT-REQUIRED`	Server to Client	402 challenge with pricing info
`PAYMENT-SIGNATURE`	Client to Server	Signed payment payload
`PAYMENT-RESPONSE`	Server to Client	Settlement confirmation

Payment Flow

Client Agent               Paid API               AgentWallex
    |                        |                         |
    |-- GET /resource ------>|                         |
    |<-- 402 + PAYMENT-REQUIRED                        |
    |                        |                         |
    |-- POST /api/v1/x402/pay -----------------------> |
    |                        |     (sign + policy)     |
    |<-- payment_info        |                         |
    |                        |                         |
    |-- GET /resource + PAYMENT-SIGNATURE -----------> |
    |<-- 200 + PAYMENT-RESPONSE                        |

Agent requests a resource

The agent sends a standard HTTP request to a paid API endpoint.

Server returns 402

The API responds with HTTP 402 and a PAYMENT-REQUIRED header containing pricing details (amount, token, chain, payTo address).

Agent pays via AgentWallex

The agent sends the payment details to POST /x402/pay. AgentWallex evaluates policies and signs the payment.

Agent retries with payment proof

The agent retries the original request with the PAYMENT-SIGNATURE header attached.

Server verifies and responds

The API verifies the payment signature (via the AgentWallex facilitator) and returns the resource.

Using x402 APIs

Check if a URL Supports x402

curl -X POST https://api.agentwallex.com/api/v1/x402/check \
  -H "X-API-Key: awx_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{"url": "https://paid-api.example.com/v1/data"}'

Create a Session Budget

Sessions let you pre-authorize a spending budget for repeated API calls:

curl -X POST https://api.agentwallex.com/api/v1/x402/sessions \
  -H "X-API-Key: awx_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "agent_id": "agent_uuid",
    "budget_limit": "100.00",
    "chain": "eip155:84532",
    "ttl_seconds": 3600,
    "allowed_urls": ["https://paid-api.example.com/v1/data"]
  }'

Trigger Payment Negotiation

curl -X POST https://api.agentwallex.com/api/v1/x402/pay \
  -H "X-API-Key: awx_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "agent_id": "agent_uuid",
    "target_url": "https://paid-api.example.com/v1/data",
    "session_id": "optional_session_uuid",
    "chain": "eip155:84532"
  }'

The response includes payment_info with:

Field	Description
`ledger_id`	Internal ledger entry ID
`amount`	Payment amount
`fee_amount`	Platform fee deducted
`fee_rate`	Fee percentage applied
`token`	Token used (e.g., USDC)
`chain`	Chain used for settlement
`status`	Payment status

SDK Integration

Automatic HTTP Interceptor

The TypeScript SDK provides an interceptor that handles the full x402 flow automatically:

const fetchWithPayment = aw.x402.httpInterceptor({
  agentId: "agent_abc123",
  chain: "eip155:84532",
});

// This automatically handles 402 challenges
const response = await fetchWithPayment("https://paid-api.example.com/v1/data");
const data = await response.json();

Manual Flow

// 1. Create a session budget
const session = await aw.x402.createSession({
  agentId: "agent_abc123",
  budgetLimit: "100.00",
  chain: "eip155:84532",
  ttlSeconds: 3600,
  allowedUrls: ["https://paid-api.example.com/v1/data"],
});

// 2. Pay for an API call
const result = await aw.x402.pay({
  agentId: "agent_abc123",
  targetUrl: "https://paid-api.example.com/v1/data",
  sessionId: session.id,
  chain: "eip155:84532",
});

// 3. Or pay using the session directly
await aw.x402.sessionPay(session.id, {
  targetUrl: "https://paid-api.example.com/v1/data",
});

For Service Providers

If you expose paid APIs, your server should return an x402 v2 challenge when payment is missing.

Return 402 with PAYMENT-REQUIRED

Encode a JSON challenge (base64) into the PAYMENT-REQUIRED header:

{
  "x402Version": 2,
  "resource": "https://your-api.com/v1/data",
  "accepts": [
    {
      "scheme": "exact",
      "network": "eip155:8453",
      "amount": "0.10",
      "asset": "USDC",
      "payTo": "0xYourAddress",
      "maxTimeoutSeconds": 300
    }
  ]
}

Verify and Settle

Use the AgentWallex facilitator endpoints:

# Verify a payment signature
POST /api/v1/x402/facilitator/verify

# Settle a verified payment
POST /api/v1/x402/facilitator/settle

# Query supported chains
GET /api/v1/x402/facilitator/supported

Operational Defaults

Parameter	Value
Settlement interval	300 seconds
Settlement threshold	$10.00
Max settlement delay	3,600 seconds
Supported chains	`eip155:84532`, `eip155:8453`, `eip155:1`, `eip155:137`

Getting Started

Platform

Core Features

Guides

What is x402?

x402 v2 Headers

Payment Flow

Using x402 APIs

Check if a URL Supports x402

Create a Session Budget

Trigger Payment Negotiation

SDK Integration

Automatic HTTP Interceptor

Manual Flow

For Service Providers

Return 402 with PAYMENT-REQUIRED

Verify and Settle

Operational Defaults

​What is x402?

​x402 v2 Headers

​Payment Flow

​Using x402 APIs

​Check if a URL Supports x402

​Create a Session Budget

​Trigger Payment Negotiation

​SDK Integration

​Automatic HTTP Interceptor

​Manual Flow

​For Service Providers

​Return 402 with PAYMENT-REQUIRED

​Verify and Settle

​Operational Defaults

What is x402?

x402 v2 Headers

Payment Flow

Using x402 APIs

Check if a URL Supports x402

Create a Session Budget

Trigger Payment Negotiation

SDK Integration

Automatic HTTP Interceptor

Manual Flow

For Service Providers

Return 402 with PAYMENT-REQUIRED

Verify and Settle

Operational Defaults