The email address doesn’t have access to this app. Try another

My app was first setup by Paul. Then I wanted to edit the app and realized I couldn’t. So we had to make it an organization app. So Paul duplicated the app, moved the copy to the organization, and deleted the old app. Then he setup the domain for the new app.

All seems to work. I can access the app using the domain. Only there is one problem:
When people try to log in, the app says: “The email address doesn’t have access to this app. Try another.” Can somebody explains what is going on?

This issue happens only when I hit the app through the custom domain. When I go directly through the glideapp URL, everything seems to work fine. Thoughts?

Thanks for your input.