If you cannot connect the authenticator and you receive the message that the "code" has already been used, it may be that the time settings on the mobile phone are not automatically synchronized with those of the internet.
This is necessary to prevent the code from being marked as expired.
You can adjust this time synchronization setting on your phone for date and time by choosing "set automatically".
For iOS: go to Settings --> General --> Date and time:
For Android: go to Settings --> General --> Date and time: