My DUO 2FA code isn't working

DUO MFA has implemented a Time-based one-time password (TOTP) that does not work with some 3rd-party authenticators and can loose sync. https://help.duo.com/s/article/6924?language=en_US

You may have luck validating the password if you let the initial DUO OTP expire and try the second code that appears.

You should also check the accuracy of the clock on the device you are using. It may have drifted too far away from the actual time and MFA solutions only accommodate a certain tolerance of clock drift. Use a site such as https://time.is/ to check how accurate your devices clock is.

Field Effect implemented the recommended time window from the TOTP protocol as a balance between security and usability. Accommodating the longer TOTP password validity that is implemented by DUO would expose a larger window to password attack.