A payment gateway is the service that takes a shopper’s payment details from your checkout, passes them securely to the banks and card networks, and returns an approval or a decline to your site. In practice, most UK providers bundle the gateway with payment processing and the merchant account that receives the money, and call the whole package a payment service provider (PSP).
How a payment gateway works
When a shopper enters a card number or taps Apple Pay, the gateway encrypts the details and sends them, through the provider’s acquiring bank, to the card network (Visa, Mastercard or American Express) and on to the bank that issued the card. If the bank asks for Strong Customer Authentication, the gateway runs the 3-D Secure step. The bank then approves or declines, the gateway tells your checkout, and the money is settled to your business account a few days later minus fees.
There are three common ways to connect:
- Hosted payment page. The shopper is sent to the provider’s page to pay and then returned to your site.
- Embedded fields. Card fields from the provider sit inside your checkout, but the card data goes straight to the provider and never touches your server.
- Direct integration. Your system handles card data itself, which brings much heavier security obligations under the PCI DSS card industry standard.
Gateways UK merchants commonly use include Stripe, PayPal and its Braintree service, Adyen, Worldpay, Checkout.com, Square and SumUp, alongside platform-run options such as Shopify Payments. These are examples, not recommendations; the right choice depends on your platform, volume and the payment methods your customers expect.
Why it matters
The gateway affects whether payments succeed, what they cost and how quickly you are paid. Fees usually combine a percentage and a fixed charge per transaction, with extra costs for some card types, non-UK cards, currency conversion, refunds and chargebacks. A low headline rate can still be the expensive option once your real mix of orders is priced in.
It also affects your payment failure rate. Good SCA support, including 3-D Secure 2 and correct handling of exemptions, lets banks approve more payments without challenging the shopper. The wallets and options a gateway supports, such as Apple Pay, Google Pay, PayPal and buy now, pay later, change how many shoppers finish paying.
Finally, it affects your data. If shoppers leave your domain to pay and come back, GA4 can credit the sale to the payment site rather than to the ad or search that brought them. That breaks attribution unless your ecommerce tracking is set up to ignore it.
Common mistakes
- Choosing on the headline percentage without pricing in fixed fees, refunds and chargebacks.
- Payment provider domains appearing as referral sources in GA4, taking credit for sales.
- The thank-you page firing the purchase event again when reloaded, producing a duplicate transaction.
- Never testing the authentication step on a phone before launch.
- Collecting card numbers by email or phone and writing them down, which creates serious security risk.
- Several payment plugins installed at once, each loading scripts on every checkout page.
How to act on it
List what you need first: the payment methods your customers use, whether you take subscriptions, whether you sell to customers outside the UK, and which ecommerce platform you are on. Then price two or three providers against last quarter’s actual orders.
Before going live, place test orders in the provider’s sandbox and with a real card on a phone. In GA4, add the payment provider’s domains to the unwanted referrals list, and confirm the purchase event fires once, with a unique transaction ID, in GBP.
Gateway setup is usually decided during a build, so I cover it in website redesign work alongside checkout design and tracking.