A free user can't log in on iOS mobile app, but can log in on desktop and web app.

My friends' account xxx@gmail.com can't log in with the mobile app, but can log in on the desktop app and web. It shows some error messages:

Sorry, access to this account is disabled. Please contact your company admin. If you are the company admin, call support at +1 (888) 8984591.

But she doesn't have the company admin. She is a free user.

How can she resolve this problem??