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What is x402?

x402 is an open HTTP payment protocol backed by Coinbase, Cloudflare, Google, Visa, Stellar, and Lightning Labs. It enables pay-per-request APIs where clients pay with crypto before accessing a resource. The protocol uses HTTP status code 402 Payment Required — a status code reserved since 1997 for exactly this purpose.

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How it Works

Client                          Server                          Chipi Paymaster
  |                               |                                |
  |  GET /api/resource            |                                |
  |------------------------------>|                                |
  |  402 + PAYMENT-REQUIRED hdr   |                                |
  |<------------------------------|                                |
  |                               |                                |
  |  [sign SNIP-12 payment]       |                                |
  |                               |                                |
  |  GET /api/resource            |                                |
  |  + X-PAYMENT header           |                                |
  |------------------------------>|                                |
  |                               |  verify + settle (gasless)     |
  |                               |------------------------------->|
  |                               |  { txHash }                    |
  |                               |<-------------------------------|
  |  200 + resource               |                                |
  |<------------------------------|                                |
  1. Client requests a protected resource
  2. Server returns 402 with a PAYMENT-REQUIRED header containing the price
  3. Client signs a USDC payment using SNIP-12 typed data
  4. Client retries the request with the signed payment in the X-PAYMENT header
  5. Server verifies the signature and settles via Chipi’s gasless paymaster
  6. Server returns the resource

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Why x402 + Chipi?

Chipi’s existing infrastructure maps perfectly to x402:
x402 ConceptChipi Infrastructure
Payment signingaccount.signMessage() (SNIP-12)
Gasless settlementPaymasterAdapter / sponsored transactions
Automated paymentsSession keys (SNIP-9)
Client walletsCHIPI / READY wallets
Key advantages:
  • Gasless: Payments are settled through Chipi’s paymaster — users never need STRK for gas
  • Session keys: Combined with SNIP-9 sessions, payments happen automatically without user interaction per request
  • Native USDC: All payments use native USDC on Starknet mainnet

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SDK Support

PackageWhat’s Available
@chipi-stack/typesTypeScript type definitions
@chipi-stack/coreX402Client — automatic 402 payment handling
@chipi-stack/backendX402Facilitator + x402Middleware for Express
chipi-reactuseX402Payment hook
chipi_sdk (Python)X402Client + X402Facilitator + middleware

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Quick Examples

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Client: Pay for APIs

import { X402Client } from "@chipi-stack/core";

const client = new X402Client(account, {
  maxPaymentAmount: "1.00", // Max $1 USDC per request
});

// Automatically handles 402 responses
const response = await client.fetch("https://api.example.com/premium-data");
const data = await response.json();

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Server: Monetize APIs

import { x402Middleware } from "@chipi-stack/backend";

const facilitator = sdk.createX402Facilitator();

app.get("/premium", x402Middleware({
  facilitator,
  paymentConfig: { amount: "0.01", payTo: "0xYOUR_ADDRESS" },
}), (req, res) => {
  res.json({ data: "premium content", txHash: req.x402.txHash });
});

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Next Steps

Client Guide

Pay for APIs from your app

Server Guide

Monetize your API endpoints

Session Keys

Automated payments with sessions