Error 403 Restricted Client with Google Signin in Flutter

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.

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.

To fix a similar issue I had to add the email I am logged in with to google as a test user:

1. Go to https://console.developers.google.com/
2. On the top right ensure that your using the correct developer account
3. On the top left next to the words "Google Cloud Platform" ensure that you are on the correct project
4. In the search bar, look for "oauth consent screen" and click on it
5. Created a consent screen if you didn't before now
6. Under "Test users" click "+ADD USERS"
7. Add the email account(s) you will be testing with and save.

It should work now!

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 everything is working.