For the next time, please provide error messages and/or logentries.
The following is a wild guess in the dark, because we’re missing information.
I assume, that your error message is:
Application-specific password required: https://support.google.com/accounts/answer/185833 (Failure)
Google changed their security setup, which does no longer allow you to authenticate against your Google Account password. To fix your issue, you’ll need to go to your account -> security and then to “App-Passwords” (logging in on google). [Link: https://myaccount.google.com/apppasswords?utm_source=google-account ]
As app choose “other” and as name something meaningfull to you, e.g. Zammad", hit generate and copy that pasword into your Zammad password field. Username will remain the same.
Worked for me.