3D Secure authentication is a fraud prevention measure designed to add an extra layer of security when you make online purchases. When you go to pay on a website and enter your payment details, you'll be redirected to your credit or debit card provider's 3D secure web page. Here, you'll be asked to enter a one-time authentication code or password, which verifies that you are the rightful owner of the card.

The authentication code is usually sent to your phone via SMS or email, depending on which service your card provider is using. You'll need to enter this code into the 3D secure page to complete the payment process. If you don't receive your code, you should contact your card provider for assistance.

Once verified, the payment will be approved and you'll be directed back to the main payment page.