3D secure authentication is intended to stop fraudsters in their tracks, but genuine cardholders may also be told that their transaction has failed to pass the protocol. This may simply be due to a typo when inputting their card number, expiry date or CVV number, or they may have entered the one-off authentication code incorrectly. There’s also the possibility of a technical issue on their computer or mobile device, with certain browser extensions known to cause issues with 3D Secure. If the issue persists, a customer’s best course of action is to contact their bank or card issuer for advice.