Why must I enter a second confirmation code?

There are two reasons why this can happen. The server cannot determine which applies, at least not without giving any clues to potential crackers. It can decide after you enter a second confirmation code.

The first situation is mistyping your confirmation code. If this happens, the server will accept it if you enter the next code properly. Do not retry with a corrected version of the failing code.

The second situation is if the server and card ran out of sync. If this happens, the server will accept a sequence of two confirmation codes in immediate succession.

In both cases, all you have to do is enter a second confirmation code. Be accurate, for you will be temporarily locked out if you fail twice. The lockout time will increase as you continue to make mistakes, to discourage cracking attempts.