Payments - Tozzecard

The demo merchant (/merchant/*) returns 404 until Binance approves our B402 application. The flow below is what the app runs once it is on.

B402 is Binance’s x402 facilitator on BNB Chain. A merchant server answers 402 Payment Required with its terms; the payer signs; the merchant asks B402 to verify and settle. B402 submits the transaction and pays the gas, and the funds go straight to the merchant’s payTo address.

Create an order

const order = await fetch(`${API}/merchant/orders`, {
  method: "POST",
  headers: { "content-type": "application/json" },
  body: JSON.stringify({ amount: "1.50", description: "Coffee" }),
}).then((r) => r.json());
const orderId = order.id;

Pay it

import { paymentHeader, transferAuthorization } from "@tozzecard/binance/eip3009";

const payUrl = `${API}/merchant/orders/${orderId}/pay`;

// 1. The merchant answers 402 with what it accepts.
const { accepts } = await fetch(payUrl).then((r) => r.json());
const req = accepts[0];

// 2. The card signs a USD1 transfer authorization for exactly that.
const { authorization, typedData } = transferAuthorization(req, account.address);
const signature = await account.signTypedData(typedData);

// 3. Send it back; the merchant verifies and settles through B402.
const res = await fetch(payUrl, {
  method: "POST",
  headers: { "PAYMENT-SIGNATURE": paymentHeader(payUrl, req, authorization, signature) },
});
const order = await res.json(); // status: "paid", tx: BSC tx hash

The card holds no BNB at any point: B402 submits the transaction and pays the gas.

Why USD1

B402 accepts U and USD1 through EIP-3009: a signed transfer, no approval, no gas for the payer. USDT and USDC go through Permit2 instead, which needs a one-time approval that costs gas. The card uses USD1 so it never holds BNB.

Header	Direction	Content
`PAYMENT-SIGNATURE`	Request	The signed authorization, from `paymentHeader()`
`PAYMENT-RESPONSE`	Response	B402’s settlement receipt