It seems that your OAuth client got deleted from your console, there's a similar question regarding this issue in the following link. You can check that by heading to the APIs & Services menu, under the Credentials topic.
Quoting the provided solution there:
You need to restore (if possible) or re-create it.
Dashboard -> Enable APIs and get credentials like keys -> Credentials -> New Credentials -> OAuth Client ID
Add the new client id and Reversed Client id to GoogleService-Info.plist
Finally add com.googleusercontent.{apps.YOUR_CLIENT_ID} to URLSchemes