An extra verification step the customer's bank requests during online card payments, often a code on the phone or approval in the bank app.
3D Secure is a protocol that adds a layer of protection to online card payments. At checkout, the issuing bank may ask the customer to confirm their identity with a code sent to their phone or an approval in the bank app. Newer versions try to skip this step for low-risk transactions.
The extra check reduces fraud and disputed payments, and in many cases banks or networks require it. But it is an added step that can fail if the window is unclear or slow on mobile, or if the code expires.
Practical tip: choose a gateway that handles this step smoothly inside your app and on phones, and test it with different card types. Track payments that fail at this stage specifically; they point to an experience problem, not a lack of customer intent.