Pay an API call with 1 USDC.

import { createWalletClient, http, parseSignature } from "viem";
import { base } from "viem/chains";
import { privateKeyToAccount } from "viem/accounts";

const USDC_BASE = "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913";
const account = privateKeyToAccount(process.env.PRIVATE_KEY as `0x${string}`);
const wallet = createWalletClient({ account, chain: base, transport: http() });

// 1. Discover live endpoints
const discovery = await fetch("https://app.suedeai.ai/.well-known/x402.json")
  .then((r) => r.json());

// 2. First call returns 402 with payment requirements
const unpaid = await fetch("https://app.suedeai.ai/create-music", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({ prompt: "lofi beat", durationSeconds: 120 }),
});
const challenge = await unpaid.json();
const req = challenge.accepts[0];

// 3. Sign EIP-3009 TransferWithAuthorization
const now = Math.floor(Date.now() / 1000);
const authorization = {
  from: account.address,
  to: req.payTo,
  value: BigInt(req.amount),
  validAfter: BigInt(Math.max(0, now - 600)),
  validBefore: BigInt(now + (req.maxTimeoutSeconds ?? 300)),
  nonce: `0x${crypto.randomUUID().replace(/-/g, "")}${"00".repeat(8)}` as `0x${string}`,
};
const signature = await wallet.signTypedData({
  account,
  domain: { name: "USD Coin", version: "2", chainId: 8453, verifyingContract: USDC_BASE },
  types: { TransferWithAuthorization: [
    { name: "from", type: "address" }, { name: "to", type: "address" },
    { name: "value", type: "uint256" }, { name: "validAfter", type: "uint256" },
    { name: "validBefore", type: "uint256" }, { name: "nonce", type: "bytes32" },
  ]},
  primaryType: "TransferWithAuthorization",
  message: authorization,
});

const xPayment = Buffer.from(JSON.stringify({
  x402Version: 2, scheme: req.scheme, network: req.network,
  payload: { authorization, signature },
})).toString("base64");

// 4. Retry with X-Payment header, asset is delivered
const paid = await fetch("https://app.suedeai.ai/create-music", {
  method: "POST",
  headers: { "Content-Type": "application/json", "X-PAYMENT": xPayment },
  body: JSON.stringify({ prompt: "lofi beat", durationSeconds: 120 }),
});
const asset = await paid.json();
console.log(asset.url);