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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.

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x402 v2 Headers

The protocol uses three HTTP headers:
HeaderDirectionPurpose
PAYMENT-REQUIREDServer to Client402 challenge with pricing info
PAYMENT-SIGNATUREClient to ServerSigned payment payload
PAYMENT-RESPONSEServer to ClientSettlement confirmation

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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                        |
1

Agent requests a resource

The agent sends a standard HTTP request to a paid API endpoint.
2

Server returns 402

The API responds with HTTP 402 and a PAYMENT-REQUIRED header containing pricing details (amount, token, chain, payTo address).
3

Agent pays via AgentWallex

The agent sends the payment details to POST /x402/pay. AgentWallex evaluates policies and signs the payment.
4

Agent retries with payment proof

The agent retries the original request with the PAYMENT-SIGNATURE header attached.
5

Server verifies and responds

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

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Using x402 APIs

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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"}'

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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"]
  }'

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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:
FieldDescription
ledger_idInternal ledger entry ID
amountPayment amount
fee_amountPlatform fee deducted
fee_rateFee percentage applied
tokenToken used (e.g., USDC)
chainChain used for settlement
statusPayment status

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SDK Integration

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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();

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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",
});

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For Service Providers

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

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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
    }
  ]
}

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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

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Operational Defaults

ParameterValue
Settlement interval300 seconds
Settlement threshold$10.00
Max settlement delay3,600 seconds
Supported chainseip155:84532, eip155:8453, eip155:1, eip155:137