Payment gateway integration is not simply a matter of putting a “Pay Now” button on a checkout page. It has to connect your website, payment provider, customer, order system, and bank or card network in a way that is secure and reliable.
For a business that already has a working website, the good news is that you usually do not need to rebuild the entire website to accept online payments. Instead, a payment gateway can be integrated into an existing website by connecting the gateway’s APIs or checkout tools with your current order and payment flow.
Whether you run an eCommerce store, service business, booking website, membership platform, or custom web application, the basic process remains similar, and a website development company in Chandigarh can help you with this.
What Is a Payment Gateway, and How Does Payment Gateway Integration Work?
A payment gateway is the technology that allows a website to accept digital payments from customers.
When a customer enters payment details and completes a transaction, the gateway securely communicates between your website and the payment system. It helps process the transaction and sends the payment status back to your website.
Depending on the gateway and payment methods you enable, customers may be able to pay using:
- Credit and debit cards
- UPI
- Net banking
- Digital wallets
- Bank transfers
- EMI or other supported payment methods
- International cards and currencies, where available
The payment gateway itself does not replace your website’s order system. Your website still needs to know what the customer purchased, how much they paid, whether the payment succeeded, and what should happen after the transaction.
Can Payment Gateway Integration Be Added to an Existing Website?
Yes. A payment gateway can usually be integrated into an existing website without changing the complete website structure.
For businesses looking for a local development partner, choosing an experienced website development company in Chandigarh can make payment gateway integration easier, particularly when the existing website is custom-built and requires changes to the backend, database, or checkout process.
The exact method depends on how your website was developed. For example, integration can be different for:
- WordPress websites
- WooCommerce stores
- Shopify stores
- Laravel applications
- PHP websites
- Node.js applications
- React-based applications
- Python/Django websites
- Custom-built websites
A ready-made plugin may be enough for some platforms, while a custom-developed website may require API integration.
Before starting the integration, the developer should first understand how your existing website handles products, orders, customers, invoices, and payments.
How to Integrate a Payment Gateway Into an Existing Website
1. Choose the Right Payment Gateway
The first step in any payment gateway integration project is choosing a provider that matches your business requirements.
Do not select a gateway only because another website is using it. Instead, look at the payment methods it supports, transaction charges, settlement process, documentation, refund facilities, and integration options.
For an Indian business, you may want to consider gateways that support UPI, cards, net banking, and other commonly used payment methods.
If you sell internationally, additional questions become important:
- Does it support international cards?
- Which currencies can customers use?
- Are international transactions enabled?
- How are settlements handled?
- What verification is required?
- Does it support recurring payments if your business needs subscriptions?
The payment gateway should fit the business model, not the other way around.
2. Create a Merchant Account
After selecting a gateway, you generally need to create a merchant account and complete the provider’s verification process.
The exact documentation depends on the payment provider and type of business.
Once the account is approved, you normally receive credentials required for integration. These may include an API key, secret key, merchant ID, or other authentication credentials.
These credentials are important because they allow your website’s backend to communicate with the payment gateway.
Never expose secret API credentials in frontend HTML, JavaScript, public repositories, or browser-side code. This is one of the most important technical points in payment gateway integration.
3. Understand Your Existing Order Process
Before writing integration code, examine how your existing website creates and manages orders.
Suppose a customer purchases a product worth ₹2,500. Your system should be able to establish something similar to:
Customer → Cart → Order Created → Payment Initiated → Payment Verified → Order Confirmed
The order should not automatically become “paid” simply because the customer reached a payment page.
Your database should normally maintain a payment status such as:
- Pending
- Processing
- Successful
- Failed
- Cancelled
- Refunded
This makes it easier to handle real-world situations, such as a customer being charged while the browser fails to return to your website.
4. Use the Payment Gateway’s API or Checkout Integration
Most modern payment providers offer APIs and documentation for developers. There are generally two common approaches to payment gateway integration.
Hosted Checkout
With hosted checkout, the customer is redirected to a payment page provided by the payment gateway or an embedded checkout component. This approach can reduce the amount of sensitive payment handling your website needs to implement, making it a practical choice for businesses that want a faster and simpler integration.
API-Based Custom Integration
With API-based integration, your website communicates directly with the gateway’s API. This gives developers greater control over the payment flow and user experience. However, it also requires more careful development around:
- Authentication
- Order creation
- Payment verification
- Webhooks
- Error handling
- Security
- Refunds
- Transaction records
For a custom website, API integration is often useful when the standard checkout flow does not fit the business requirements.
5. Create the Payment Order on the Server
A common mistake is treating the amount displayed on the browser as the final payment amount.
For example, a product page may show a product price of ₹4,000. But the final amount could change because of:
- Discount
- Coupon
- Tax
- Shipping
- Additional service charges
The final amount should therefore be calculated and validated on the server. Your backend can then create the payment order with the gateway using the verified amount — this prevents customers from manipulating frontend values before payment.
6. Send the Customer to the Payment Screen
Once the payment order has been created, the website can initiate the checkout process.
The customer selects a payment method and completes the transaction. At this stage, several things can happen:
Payment succeeds — The gateway reports a successful transaction.
Payment fails — The transaction is rejected or fails because of a bank, card, UPI, authentication, or other issue.
Customer closes the payment window — The transaction may remain pending or may never be completed.
Money is deducted but your website shows failure — This is one of the situations developers must plan for carefully.
You cannot assume that the browser’s response alone represents the final truth about the transaction.
7. Verify the Payment on Your Server
Payment verification is one of the most important parts of the entire payment gateway integration process.
After the customer completes payment, your backend should verify the transaction using the information returned by the payment gateway. Depending on the provider, verification may involve:
- Payment/order ID
- Transaction ID
- Signature
- API verification
- Gateway response
- Webhook confirmation
The exact implementation depends on the payment gateway. The key principle is simple: do not mark an order as paid based only on information coming from the customer’s browser.
Your server should independently verify that the transaction is genuine and that the amount and order information match your records.
8. Configure Webhooks
A webhook allows the payment gateway to send information directly to your server when a payment event occurs. This is particularly useful when the customer does not return to your website after completing payment.
For example, a customer pays ₹3,000. The bank completes the transaction. Before the customer is redirected back to your website, their internet connection drops. If your website depends only on the browser redirect, your order could remain marked as unpaid even though the transaction succeeded.
A webhook can notify your server about the payment status, and your backend can then update the order accordingly. Webhooks are therefore an important part of a reliable payment gateway integration.
9. Update the Order After Successful Payment
Once the payment has been properly verified, your website can perform the required business action.
For an eCommerce website, that may mean:
- Marking the order as paid
- Reducing inventory
- Generating an invoice
- Sending an order confirmation
- Updating the customer’s account
- Starting the shipping process
For a booking website, it could mean confirming an appointment or reservation. For a subscription platform, the system may activate the customer’s subscription.
The payment gateway confirms the transaction, but your website decides what that successful transaction means for your business.
10. Handle Failed and Duplicate Payments
Payment gateway integration should not be designed only for successful transactions. Real customers will encounter failures.
Your system should be prepared for:
- Failed payments
- Cancelled payments
- Expired sessions
- Duplicate requests
- Duplicate webhook notifications
- Network failures
- Payment completed but redirect failed
- Refunds
- Partial refunds, where supported
- Delayed payment confirmations
Your developer should also make the payment process idempotent, meaning the same payment notification or request should not accidentally create two orders or charge a customer twice. This is especially important for busy eCommerce websites.
What Technology Is Needed for Payment Gateway Integration?
The technology depends on your website. For example:
- A PHP or Laravel website may use the payment provider’s PHP SDK or REST APIs.
- A Node.js application can communicate with the gateway through Node.js libraries or API requests.
- A Python application can use the provider’s Python SDK or APIs.
- WordPress and WooCommerce websites often have gateway plugins available, although custom development may still be required for special requirements.
- The frontend may use HTML, CSS, and JavaScript for the checkout interface, while the backend handles authentication, order creation, verification, and database updates.
The important point is that payment processing should not be treated as a frontend-only feature.
Is Payment Gateway Integration Secure?
Security should be considered before the integration goes live, not after the first transaction. Some important practices include:
Use HTTPS — Your website should use a valid SSL/TLS certificate and load through HTTPS.
Protect API credentials — Secret keys should remain on the server and should never be exposed through frontend code.
Validate payment amounts — Do not blindly trust prices or totals received from the browser.
Verify transaction responses — Your backend should verify payment information using the gateway’s recommended method.
Validate webhooks — Webhook requests should be authenticated or verified according to the payment provider’s documentation.
Keep payment records — Store the relevant transaction identifiers and status information so payments can be traced later.
Follow the gateway’s security requirements — Payment providers may have specific requirements around authentication, tokenisation, data handling, and compliance. Most gateways require merchants to follow the PCI Data Security Standard, the global benchmark for handling card data securely, so developers should follow the current documentation provided by the selected gateway alongside it.
How Much Does Payment Gateway Integration Cost?
There is no single price for payment gateway integration. Many providers don’t charge a separate monthly fee for the basic gateway. Instead, they typically charge a transaction fee (MDR/platform fee) on successful payments.
If the existing website has no proper order management or payment architecture, additional development may be required before the gateway can be connected.
Also remember that development cost and payment gateway transaction charges are separate things. The gateway may charge fees per transaction or according to its current pricing structure.
Payment Gateway Integration for Businesses in Chandigarh
A professional web designing company in Chandigarh can also help improve the checkout experience so that the payment process is simple, responsive, and easy to understand on both desktop and mobile devices.
The important thing is not simply finding someone who can connect an API. Rather, the developer should understand your existing website architecture and the complete journey from order creation to payment confirmation.
Common Mistakes to Avoid During Payment Gateway Integration
Using Only the Frontend Response — A frontend response should not be treated as the final confirmation of a successful payment.
Exposing Secret Keys — Private credentials should never be placed inside JavaScript that can be viewed by website visitors.
Not Testing Failed Transactions — Testing only successful payments gives a false sense of security. Your testing should cover failed, cancelled, pending, and interrupted transactions as well.
Ignoring Webhooks — A redirect-based payment flow can fail when a customer loses connectivity or closes the browser. Webhooks provide an additional server-to-server mechanism for receiving payment updates.
Not Maintaining Transaction IDs — Transaction and order identifiers make it easier to investigate disputes, refunds, failed payments, and customer complaints.
Treating Every Webhook as a New Payment — Payment gateways may send repeated notifications. Your system should check whether the transaction has already been processed before updating the order again.
Testing Before Going Live — Never connect a payment gateway to a production website and immediately start accepting real transactions. Instead, use the provider’s test or sandbox environment whenever available.
Test scenarios such as:
- Successful card payment
- Failed card payment
- Successful UPI payment
- Cancelled transaction
- Customer closing checkout
- Incorrect payment details
- Slow internet connection
- Payment completed but redirect interrupted
- Duplicate webhook
- Refund
- Order amount mismatch
- Multiple payment attempts for one order
After testing, verify the complete flow from the customer side and from the website’s admin panel.
What Happens After Payment Gateway Integration?
Once the integration is working, the payment process becomes part of your website’s regular business workflow. A typical process looks like this:
Customer selects product/service → Website calculates final amount → Order is created → Payment gateway order is generated → Customer completes payment → Gateway sends payment response → Server verifies transaction → Webhook confirms status where applicable → Website updates order → Customer receives confirmation
This sequence may look simple to the customer, but several backend processes are working behind the scenes.
Frequently Asked Questions
Can I add a payment gateway to my existing website? Yes. In most cases, a payment gateway can be added to an existing website without rebuilding the complete website. The integration method depends on your website platform, backend technology, and business requirements.
Do I need to change my existing website? Not necessarily. If your existing website already has a proper product, cart, and order structure, the developer may only need to add the payment functionality and connect it with the existing workflow.
Can I integrate UPI payments into my website? Yes, if the selected payment gateway supports UPI and your merchant account is eligible for the relevant payment methods.
Can a payment gateway support international payments? Some payment gateways support international transactions, but availability depends on the provider, merchant account, business type, country, and currency requirements.
Is a payment gateway API difficult to integrate? The complexity depends on the website. A simple integration may be relatively straightforward, while a custom eCommerce or subscription platform can require considerably more backend work.
Should payment verification happen on the frontend? No. Important payment verification should be performed on the server using the gateway’s recommended verification process.
Why are webhooks important? Webhooks allow the payment provider to notify your server about payment events even when the customer does not successfully return to your website.
Can I add more than one payment gateway? Yes, a website can be designed to support multiple gateways, depending on the business requirements and technical architecture.
What happens if a customer is charged but the order remains pending? The transaction should be checked against the gateway’s records. Webhook notifications, server-side verification, and transaction IDs can help reconcile the payment and update the order correctly.
Can payment gateway integration be added to WooCommerce? Yes. WooCommerce supports payment gateway integrations through extensions and custom development. The right approach depends on the gateway and the level of customisation required.
Can I integrate a payment gateway into a Laravel website? Yes. Laravel applications can connect to payment gateways through official SDKs, third-party libraries, or REST APIs, depending on what the payment provider offers.
How long does payment gateway integration take? There is no fixed timeline. A basic integration may take less time than a custom payment system involving subscriptions, multiple gateways, international payments, refunds, and a complex order management system.
Do I need SSL for online payments? Your website should use HTTPS for secure communication. Payment providers may also have additional security and compliance requirements that need to be followed.
Can I customise the payment page? It depends on the payment gateway and integration method. Hosted checkout solutions may offer limited customisation, while some APIs provide greater control over the user interface.
What information should my website store after payment? Your system generally needs enough transaction and order information to identify the payment, update the order, and handle customer support, reconciliation, and refunds. Sensitive payment credentials or card information should not be stored unless the relevant architecture and compliance requirements specifically permit it.
Can I integrate payment gateway and invoice generation together? Yes. After a successful and verified transaction, your website can trigger invoice generation and send the invoice or payment confirmation to the customer.
What should I check before selecting a payment gateway? Look at supported payment methods, transaction charges, settlement process, international payment support, refund capabilities, recurring payment options, documentation, developer support, and compatibility with your existing website.
