There are several reasons why this might be happening.

1. Check the app version:
   Make sure you’ve downloaded the correct mobile app - FitKit. Using an older or localized version such as FitKit GR, FitKit MK, FitKit RS, or MyFitKit might cause login issues.

2. Existing account:
   Recall whether you have already created an account with the email address you are trying to log in with. It’s possible you are using the wrong email address, especially if you have multiple accounts.

3. Deleted account:
   If you are certain you are using the correct email address, it’s possible your account was deleted and no longer exists in our database. In this case, you will need to create a new account.

4. Password issues:
   If you try to create a new account and receive a message that the email address already exists but you cannot remember the password, try resetting your password. For more information, visit the following link.

5. Third-party logins:
   If you previously chose to log in using Google, Facebook, or Apple ID, attempts to log in with an email address or reset the password will fail. In this case, try logging in again using the same platform.