You configured 2 factor authentication with google, and now you can't login to Nebula / MyZyxel because you lost the Google authenticator!
If so, you can switch to mail verification temporarily for 2 factor authentication
1) Enter the wrong OTP code at the first time,
2) Then click the link "Failed to get verification codes
3) Go trough the options by clicking the arrow and choose Email verification and click send
4) Open you're email and copy the code, fill this code into the verification field