A different domain requests login

When I use one of the domains that isn't the main one where WordPress is installed for a non-admin user, it requests a login to view the dashboard, even if I'm logged in as admin.

This is for each domain. I did a test on two different domains, but for the same non-admin user, and it wouldn't let me view either of the sites without logging in. The 'sites' show in the sites dropdown, but it goes to the login page.