3D authentication is an extra layer of security used by credit and debit card issuers for transactions that are made online.
You'll see it as a pop-up in the form of Verified by Visa or MasterCard Secure, and you'll be asked to enter a code or pin that will be sent to you by your card issuer via email or SMS. This adds an extra layer of authorization to online payments.
If you receive an error message that your 3D secure failed, check that you entered your passcode correctly and that the passcode hasn't expired. If you did not receive a passcode, call your bank.
Some card issuers will automatically enable 3D authentication while others will require you to activate it. If you don't already have 3D authentication on your card and you'd like to add extra security and fraud protection to your credit or debit card, contact your card issuer directly and ask them how to add 3D authentication.