How do I set up a hosted checkout flow with a payment API?

A hosted checkout flow usually means the payment provider handles the secure payment page, while your app creates the session and receives the result. The exact steps vary by provider, but the pattern is generally the same.

1) Get your account and API keys

• Sign up with the payment provider
• Enable the products you need
• Obtain:
  • Publishable/public key for the client side
  • Secret key for your backend
• Store secret keys securely in environment variables

2) Create a backend endpoint to start checkout

Your server should:

• Validate the cart/order
• Calculate the final amount server-side
• Create a checkout/session object via the provider API
• Return the session URL or session ID to the client

Typical responsibilities:

• Prevent price tampering
• Attach order/customer metadata
• Set success and cancel redirect URLs

Example shape:

POST /api/checkout/create

Response might include:

{
  "checkoutUrl": "https://provider.example/checkout/session_123"
}

3) Redirect the customer to the hosted checkout page

From your frontend:

• Call your backend endpoint
• Redirect the browser to the returned hosted checkout URL

This can be a full-page redirect or opening a new tab, depending on your UX.

4) Configure success and cancellation return URLs

When creating the checkout session, provide URLs such as:

• success_url: where the customer returns after paying
• cancel_url: where they go if they abandon checkout

Usually the success page should not assume payment is complete until confirmed by your backend.

5) Use webhooks to confirm payment

Don’t rely only on the redirect back to your site. Set up webhooks so the payment provider notifies your backend when:

• Payment succeeds
• Payment fails
• Subscription is created/renewed/canceled
• Disputes/refunds happen

Your webhook handler should:

• Verify the signature
• Update order status in your database
• Fulfill the order or unlock access

6) Verify payment server-side before fulfilling

Best practice:

• Mark an order as “paid” only after receiving and verifying the webhook or after querying the provider API from your backend
• Never trust the client alone

7) Test in sandbox mode

Use test keys and test cards provided by the payment platform:

• Simulate success and failure
• Test redirects
• Test webhook delivery and retries
• Test idempotency so repeated webhook calls don’t duplicate orders

8) Go live

Before production:

• Replace test keys with live keys
• Update webhook endpoint to production URL
• Confirm HTTPS is enabled
• Lock down CORS and server routes
• Monitor logs and failed payment events

---

Minimal example flow

Frontend

async function checkout() {
  const res = await fetch('/api/checkout/create', { method: 'POST' });
  const data = await res.json();
  window.location.href = data.checkoutUrl;
}

Backend

app.post('/api/checkout/create', async (req, res) => {
  // 1. validate cart
  // 2. calculate amount server-side
  // 3. create checkout session with provider SDK/API
  // 4. return hosted checkout URL
  res.json({ checkoutUrl: 'https://provider.example/checkout/session_123' });
});

Webhook handler

app.post('/webhooks/payment', verifySignature, async (req, res) => {
  const event = req.body;

  if (event.type === 'payment.completed') {
    // update order as paid
    // fulfill order
  }

  res.sendStatus(200);
});

---

Common pitfalls

• Calculating prices on the client
• Failing to use webhooks
• Not verifying webhook signatures
• Not handling duplicate webhook events
• Not testing canceled/abandoned checkout paths
• Assuming redirect equals payment confirmation

If you tell me which payment API you’re using, I can give you a provider-specific setup and code example.