Hello YaxmanTDY,
Please check if your smartphone (where the 2FA App is installed) and your computer (where you are trying to sign in) are in "time-sync".
Check on both devices the time, by opening this site:
https://time.is
If they are seconds away from each other, it could be possible that the code is rejected (you need also some time to enter the code and the codes are valid only for 30 seconds).
If everything is ok, but you're still not able to sign in, then contact us via support(at)boxcryptor.com by referring to the post here.
Best,
Yasmin