x402 Payment Protocol

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               |                                |
  |<------------------------------|                                |

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();

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 });
});