// server.js (Node.js example)
app.post('/checkout/initiate', async (req, res) => {
  const { orderId, amount } = req.body;
  
  const response = await fetch('https://api.settlx.io/api/v1/invoices', {
    method: 'POST',
    headers: {
      'Authorization': `Bearer ${process.env.SETTLX_API_KEY}`,
      'Content-Type': 'application/json'
    },
    body: JSON.stringify({
      amount: amount.toString(),
      currency: 'USD',
      description: `Order #${orderId}`,
      expiresInMinutes: 30,
      webhookUrl: `${process.env.BASE_URL}/webhooks/settlx`,
      metadata: { orderId }
    })
  });
  
  const { data: invoice } = await response.json();
  
  // Save invoice ID for later lookup
  await db.orders.update({
    where: { id: orderId },
    data: { settlxInvoiceId: invoice.id }
  });
  
  // Redirect customer to hosted checkout
  res.redirect(invoice.paymentUrl);
});

// Webhook handler
app.post('/webhooks/settlx', express.raw({ type: 'application/json' }), async (req, res) => {
  // Verify signature (recommended)
  const signature = req.headers['x-webhook-signature'];
  if (!verifySignature(req.body, signature, process.env.SETTLX_WEBHOOK_SECRET)) {
    return res.status(401).send('Invalid signature');
  }
  
  const event = JSON.parse(req.body);
  
  switch (event.event) {
    case 'invoice.settled': {
      // Funds are in your wallet — safe to fulfill the order
      const orderId = event.data.invoice.metadata?.orderId;
      await fulfillOrder(orderId);
      break;
    }

    case 'invoice.expired': {
      // Payment was not received within the expiry window
      const orderId = event.data.invoice.metadata?.orderId;
      await markOrderExpired(orderId);
      break;
    }
  }
  
  res.status(200).send('OK');
});

// Include return URLs in metadata
body: JSON.stringify({
  amount: '99.99',
  currency: 'USD',
  metadata: {
    orderId: '1234',
    successUrl: 'https://yoursite.com/order/1234/success',
    cancelUrl: 'https://yoursite.com/order/1234/cancel'
  }
})