How to Integrate Khalti Payment Gateway in Node.js and Laravel (ePayment API v2)

# Khalti Credentials
KHALTI_SECRET_KEY=live_secret_key_68791341fdd94846a146f0457f9b6e1b # Replace with your test/live key
KHALTI_API_BASE=https://a.khalti.com/api/v2
APP_URL=http://localhost:3000

const axios = require('axios');

async function initiateKhaltiPayment({ returnUrl, websiteUrl, amountNpr, purchaseOrderId, purchaseOrderName, customerInfo }) {
  const url = `${process.env.KHALTI_API_BASE}/epayment/initiate/`;
  
  // Convert NPR to Paisa (Rs 10 = 1000 Paisa)
  const amountInPaisa = Math.round(Number(amountNpr) * 100);

  const payload = {
    return_url: returnUrl,
    website_url: websiteUrl,
    amount: amountInPaisa,
    purchase_order_id: purchaseOrderId,
    purchase_order_name: purchaseOrderName,
    customer_info: customerInfo || {
      name: "Test Customer",
      email: "test@example.com",
      phone: "9800000000"
    }
  };

  const response = await axios.post(url, payload, {
    headers: {
      Authorization: `Key ${process.env.KHALTI_SECRET_KEY}`,
      'Content-Type': 'application/json'
    }
  });

  // response.data contains: { pidx: "...", payment_url: "https://...", expires_at: "..." }
  return response.data;
}

module.exports = { initiateKhaltiPayment };

router.get('/khalti/callback', async (req, res) => {
  const { pidx, status, transaction_id } = req.query;

  if (!pidx) return res.status(400).send('Missing pidx in callback');

  try {
    const lookupRes = await axios.post(
      `${process.env.KHALTI_API_BASE}/epayment/lookup/`,
      { pidx },
      {
        headers: {
          Authorization: `Key ${process.env.KHALTI_SECRET_KEY}`,
          'Content-Type': 'application/json'
        }
      }
    );

    const data = lookupRes.data;

    if (data.status === 'Completed') {
      // 1. Verify data.total_amount matches expected order amount
      // 2. Mark order as Paid in database
      // 3. Prevent duplicate fulfillment
      return res.redirect(`/order-success?pidx=${pidx}`);
    } else {
      return res.redirect(`/order-failed?status=${data.status}`);
    }
  } catch (error) {
    console.error('Khalti lookup error:', error.response?.data || error.message);
    return res.status(500).send('Payment verification failed');
  }
});