Error 403 Restricted Client with Google Signin in Flutter
In my case I forgot to set support e-mail address in Google Developers Console > API and service > certificate > OAuth consent screen link and this option also in your Firebase project setting .After set up then everything is working.
I set the support e-mail address and the LOGO in Google :
Developers Console > API and service > Credential > Oauth Consent Screen.After this set up all is working.
Had a similar problem with an angular project. The solution was indeed to set a support email address in the firebase console project settings under the general tab.