Why is my personal key invalid?
A personal key is a 16-character secret code we give you when you create an account. The personal key is the only way to sign in if you lose access to the device you use for two-factor authentication. You can only use your personal key once. You will receive a new personal key each time you use it to sign in, and your old one will no longer work.
If you are being told your personal key is invalid, you have either typed it in incorrectly or you have already used it to sign in and it is no longer valid. If you have already used your personal key to sign in, you were given a new one that must be used to sign in.