Reviewed by Mayer Hyman, Payments Specialist | Reviewed for accuracy July 2026
Key Takeaways
- Digital payments rely on an API connecting the merchant’s software to a payment gateway and processor behind the scenes, invisible to both the shopper and the merchant in most transactions.
- HTTP GET requests expose transaction data in the URL, browser history, and server logs, making them fundamentally unsuited to handling cardholder data.
- HTTP POST requests keep transaction data in the message body, out of the URL and browser cache, which is why POST is the standard for PCI-compliant payment integrations.
- PCI DSS 4.0.1, in force since March 2025, requires automated detection of attacks on payment pages and safeguards against common API attack types like injection and cross-site scripting.
How Digital Payments Actually Move Behind the Scenes
Digital payments move behind the scenes through a payment integration: an API (Application Programming Interface) that lets merchants accept payments directly within their platform or software application by connecting a payment terminal or gateway to the payment processor. That integration is what keeps digital payments growing in both volume and variety, driven by convenience, software growth, and merchant demand for streamlined, contactless payment processes.
As consumers, we take for granted how simple it is to submit a payment, and as merchants, how easily payments seem to flow. Consider an online transaction: the customer initiates a payment, their payment information is transmitted to a payment gateway, instantaneously authenticated, and the gateway returns a response telling the website or app whether the transaction was approved or declined. On the surface, a digital transaction looks like it only has two sides, the payer (cardholder) and the payee (merchant), which makes it easy to overlook the software provider who integrated the bridge between the two.
Software plays an essential role in online payments, handling the collection and transmission of sensitive payment data for secure processing. Behind the scenes of an online transaction are HTTP payment request APIs, or API calls, which are how point-of-sale software communicates with the payment gateway server and how transactional data moves between the client side (the website) and the server.
POST Method vs. GET Method: The Security Vulnerability Hiding in Your Payment Gateway Integration
Software developers are always looking for ways to improve design and usability. Developments in payment innovation have changed how we make and accept payments, but every advantage comes with a growing concern around security, data breaches, and how sensitive data is handled and transmitted. In the effort to improve payment security, card industry compliance, and cardholder data protection, some payment integrations and transaction processing methods have had to change along with it.
POST and GET are two types of HTTP requests involved in payment gateway integrations, used to transmit payment card transaction data. Many software applications historically used the GET method in their payment integrations to communicate with the payment gateway API and post payment requests. Developers often chose GET because it was simpler, faster, and improved application performance, only to later find they could no longer remain PCI compliant using it.
Why the HTTP GET Method Isn’t PCI Compliant
The GET method requests data from the server, and the query’s data is included in plain text within the URL, browser history, and server logs, exposing sensitive cardholder information anywhere that URL gets logged or cached. That leaves transaction data susceptible to interception and open to fraud.
Why the HTTP POST Method Is the Standard
The HTTP POST method submits data from the client to the server within the message body instead of the URL. While it requires additional development work, POST requests are never visible in the URL, never cached, and don’t remain in browser history, keeping sensitive payment information out of the places attackers look first.
Support for Developers in Securing Payment Processing
Every player in the payment ecosystem has a role in securing payment processing. What was once a best-practice recommendation is now a hard requirement for ecommerce transactions, driven by the inherent security risks of handling cardholder data. The current standard, PCI DSS 4.0.1, has been mandatory for merchants and payment service providers since March 2025, and it includes over 50 requirements introduced specifically to close gaps that older versions of the standard didn’t address.
Two requirements are directly relevant to how payment APIs get built: automated detection of attacks targeting payment pages, and safeguards against common software and API attack types like injection and cross-site scripting. In practice, that means an integration still relying on the GET method for transmitting payment data isn’t just a bad idea, it’s a compliance gap under the current standard.
Several major payment gateways have phased out support for the GET method entirely, requiring point-of-sale applications to update their integrations to use POST. By partnering with a payments provider that stays ahead of these requirements, software vendors can keep their integrations compliant without scrambling every time a gateway changes its rules. Cartis Payments offers secure payment gateways, fraud detection and prevention, and developer resources; contact us with questions about securing your application and reducing fraud risk for both the payer and the payee.
FAQ
Why can’t payment integrations just keep using the GET method if it’s simpler?
Because GET puts transaction data in the URL, where it ends up in browser history, server logs, and caches, all places that expose cardholder data to unnecessary risk. That directly conflicts with PCI DSS requirements, so GET-based payment integrations aren’t compliant.
Does switching from GET to POST guarantee PCI compliance on its own?
No. Using POST is necessary but not sufficient. PCI DSS 4.0.1 also requires things like automated attack detection on payment pages and protection against injection and cross-site scripting, so a compliant integration needs more than just the right HTTP method.
Who is responsible for making sure a payment API integration is secure?
Everyone in the chain shares responsibility: the software vendor building the integration, the payment gateway processing the transaction, and the payment processor handling settlement. That’s part of why choosing a payments partner that actively maintains compliance matters.
