How to Integrate Payment Gateways Into a Website
How payment flows work, why webhooks matter, how to handle failed payments and refunds, and what security and testing a payment integration needs.
Quick answer
Integrating a payment gateway means letting the gateway collect card details through a hosted page or embedded fields, creating the payment from your server, and relying on webhooks to confirm the final payment status before fulfilling the order. A solid integration also handles failed payments, retries, refunds, duplicate-charge prevention and international requirements, and is tested thoroughly in the gateway's test mode before going live.
How a Payment Flow Works
| Step | Where it happens | Why it matters |
|---|---|---|
| 1. Customer checks out | Your website | Order created in a pending state |
| 2. Payment intent created | Your server → gateway API | Amount and currency set server-side, not by the browser |
| 3. Card details entered | Gateway's hosted page or embedded fields | Card data never touches your servers |
| 4. Authentication | Customer's bank, if required | May redirect or show a challenge |
| 5. Result returned | Gateway → customer's browser | Show confirmation, but don't trust it alone |
| 6. Webhook received | Gateway → your server | Authoritative status; update and fulfill the order |
Checkout Design
Payment integration is only part of checkout. Clear totals, visible costs, trusted payment options and a short form all affect whether customers finish. The checkout optimization guide covers the conversion side; this guide focuses on the technical integration.
Keep Card Data Off Your Servers
Use the gateway's hosted checkout or embedded payment fields so card numbers go straight to the provider. This dramatically reduces your PCI DSS compliance burden and your risk. Building a flow where raw card numbers pass through your own systems is rarely justified for a typical business website.
Webhooks and Payment Status
The customer's browser can close before your confirmation page loads, and some payments confirm later. Treat the gateway's webhook as the source of truth: verify its signature, update the order, then trigger fulfillment and emails. Handle webhooks idempotently, because gateways may deliver the same event more than once.
Building a custom checkout or payment flow?
ZSpace implements payment integrations with webhook handling, failure recovery and proper testing, so orders and payments stay in sync.
Failed Payments
Declines, authentication failures and network errors are normal. Show a clear, non-technical message, keep the order recoverable, let the customer retry or choose another method, and never fulfill an unpaid order. Track failure rates, since a spike can signal an integration problem.
Refunds and Duplicate Charges
Refunds should update your order records as well as the gateway. Support partial refunds if your business needs them. Use idempotency keys when creating payments so a double-click or retry can't charge a customer twice.
Security
Keep secret API keys server-side, verify webhook signatures, calculate amounts on the server, serve everything over HTTPS, and log payment events without logging sensitive card data. The secure website development guide covers these practices in the context of the whole site.
International Considerations
Selling across borders adds currency handling, local payment methods customers expect, strong customer authentication rules in some regions, and tax. Check what your gateway supports in each target market before launch rather than after.
Testing Checklist
- Successful payment with and without bank authentication
- Declined card and insufficient funds
- Customer closes the browser before confirmation
- Duplicate webhook delivery
- Webhook with an invalid signature is rejected
- Full and partial refunds update order records
- Double-click on the pay button doesn't double charge
- Each supported currency and payment method
Want your payment flow reviewed before launch?
Talk to ZSpace about testing and hardening your payment integration.
Conclusion
A dependable payment integration keeps card data with the gateway, sets amounts server-side, treats webhooks as the source of truth, and handles failures and refunds cleanly. If you sell primarily products online, a commerce platform may handle most of this for you; see ZSpace's Shopify development work.
Common questions
A service that securely collects payment details, authorizes the payment with the card network or bank, and reports the result back to your website.