Pay for anything
with HTTP 402

import { FacilitatorClient, createPaymentGate }
  from 'x402-fac/sdk';

// Connect to your facilitator
const facilitator = new FacilitatorClient({
  baseUrl: 'http://localhost:3000'
});

// Create a payment gate
const gate = createPaymentGate({
  facilitator,
  payTo:   'addr_test1qp...',
  amount:  '2000000',   // 2 ADA
  network: 'cardano:preview',
});

// Protect any route
app.post('/api/generate', {
  preHandler: gate
}, handler);

// 1. Request resource → get 402
const res = await fetch('/api/generate');
// res.status === 402

// 2. Parse payment requirements
const requirements = parsePaymentRequired(
  res.headers.get('Payment-Required')
);

// 3. Build & sign Cardano tx
const tx = await lucid
  .newTx()
  .pay.ToAddress(requirements.payTo, {
    lovelace: BigInt(requirements.amount)
  })
  .complete();
const signed = await tx.sign
  .withWallet().complete();

// 4. Retry with payment → get 200
const paid = await fetch('/api/generate', {
  headers: {
    'Payment-Signature':
      encodePayment(signed)
  }
}); // paid.status === 200 🎉