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What is x402?

x402 is an open payment standard built on HTTP 402 Payment Required x402 lets AI agents pay programmatically, so they can complete a checkout and purchase from your store without a browser flow or human intervention. As buying behavior shifts, integrating x402 with your store helps you stay ahead of the market and align with the growing trend of AI agents.

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Official documentation

For the full specification and concepts, see:

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How it works

x402 uses standard HTTP status codes and headers:
  1. Client requests a protected resource (e.g. checkout status).
  2. Server responds with 402 Payment Required, a PAYMENT-REQUIRED header, and a JSON body describing what to pay, how much, and where.
  3. Client (or wallet/agent) signs the transaction using that information.
  4. Client retries the same request with a PAYMENT-SIGNATURE header containing the Base64-encoded proof.
  5. Server verifies the payment and responds with 200 OK and, on success, a PAYMENT-RESPONSE header confirming settlement.

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x402 on Zeno Bank

The following endpoint supports x402 for paying for a checkout.

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POST /api/v1/checkouts/:checkoutId

BehaviorDescription
First request (no payment)HTTP 402 Payment Required with PAYMENT-REQUIRED header and payment instructions.
Retry with paymentSame POST with PAYMENT-SIGNATURE (Base64 proof). Server verifies and returns 200 + checkout + PAYMENT-RESPONSE.
Path parameter
  • checkoutId (string, required) — Checkout ID (e.g. from Create Checkout).
Example: first request (no payment) 
curl -i -X POST https://api.zenobank.io/api/v1/checkouts/ch_2wlOcI7sKr9McroZb
Example response (402)
  • Status: 402 Payment Required
  • Header: PAYMENT-REQUIRED: <Base64-encoded payment requirements>
  • Body: JSON with payment requirements. Example:
{
  "x402Version": 2,
  "resource": {
    "url": "https://api.zenobank.io/api/v1/checkouts/ch_2wlOcI7sKr9McroZb",
    "description": "Checkout ch_2wlOcI7sKr9McroZb (order: order-123)",
    "mimeType": "application/json"
  },
  "accepts": [
    {
      "network": "eip155:84532",
      "scheme": "exact",
      "asset": "0x036CbD53842c5426634e7929541eC2318f3dCF7e",
      "maxTimeoutSeconds": 300,
      "extra": { "name": "USDC", "version": "2" },
      "amount": "2000000",
      "payTo": "0xfde61cfd236328c3a136a9f876f1ab3e3a6fafe9"
    }
  ]
}
Amount is in the token’s smallest unit. USDC has 6 decimals, so "amount": "2000000" = 2 USDC.
Example: retry with payment 
curl -i -X POST https://api.zenobank.io/api/v1/checkouts/ch_2wlOcI7sKr9McroZb \
  -H "PAYMENT-SIGNATURE: <Base64-encoded payment payload>"
Example response (200)
  • Status: 200 OK
  • Header: PAYMENT-RESPONSE: <Base64-encoded settlement response>
  • Body: Checkout object. Example:
{
  "id": "ch_2wlOcI7sKr9McroZb",
  "orderId": "order-1769920141831-vscv3n6",
  "priceCurrency": "USD",
  "priceAmount": "2",
  "status": "COMPLETED",
  "expiresAt": "2026-02-01T04:49:01.908Z",
  "checkoutUrl": "https://pay.zenobank.io/ch_2wlOcI7sKr9McroZb",
  "createdAt": "2026-02-01T04:29:01.900Z",
  "successRedirectUrl": null
}

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Supported networks and assets

NetworkAssetCAIP-2 Chain IDZeno Chain ID
Base MainnetUSDCeip155:8453BASE_MAINNET
More tokens will be added over time.