Troubleshooting Sign-In using Google
From WHMCS Documentation
Google Sign-In is unavailable at this time. Please try again later.
- OR -
Google Sign-In is unavailable at this time. Please try again later. Error: Not a valid origin for the client: http://example.com has not been whitelisted for client ID xxxxx
If you receive this error message when attempting to Sign in using Google, this indicates that the URL configured within your Google App is no longer valid.
You will only receive the second more verbose error message when logged in as an admin user and attempting to use the client area Google Sign In option. To verify the cause of the error, we recommend attempting to login while authenticated as an admin user.
Please refer to Configuring Sign-In using Google for instructions regarding how to set the URL for your Google API App.