I created a Google Project to allow Google users to authenticate via Google to our O365 SharePoint Online site that we shared with our client external users.
If a user uses a Gmail account they can log in. However, our client has a custom Google domain and it does not get redirected to the Google login for authentication. It goes to the default MS Login.
How can I "register" their domain as a Google domain so they won't be directed to Microsoft login?
