I can no longer log in - The login page requires 2-factor verification

If you want to log in and a pop-up window with the heading "2-factor verification" appears, you have previously activated this security feature with your smartphone and an authenticator app (Google Authenticator or Microsoft Authenticator app). 

Caution:
Please note that two-factor authentication is a security component that cannot be easily deactivated if Eponet is used incorrectly. It can only be activated with the Google or Microsoft authenticator app – and therefore can only be deactivated with the same app.

If, for any reason, you are unable to deactivate it, it can be reset for a fee as described here.