My 2FA code isn't working ("Incorrect Code" errors)

On Android:
Go to the Main Menu on the Google Authenticator app;
Select Settings;
Select Time correction for codes;
Select Sync now.

On iOS (Apple iPhone):
Go to the iPhone Settings App (your phone settings area);
Select General;
Select Date & Time;
Enable Set Automatically;
If its already enabled, disable it, wait a few seconds and re enable.