There are a bunch of reasons why this type of error may be reported. From the screenshot shared, I see no issues with your setup trying to change return URI in your google console for OAuth2, which is why I recommend this issue is reported by contacting the GCP Support Engineers[1] or you open an issue using this link[2].
[1]https://cloud.google.com/support-hub [2]https://developers.google.com/issue-tracker/#public_users -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To unsubscribe from this group and stop receiving emails from it, send an email to google-appengine+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/google-appengine/358a56ad-f45c-4d44-9aaf-33ed5754a719%40googlegroups.com.
