I am using hosting beta
defender->Advanced tools->MASK LOGIN AREA
I set a new URL and Enable 404 redirection
Any attempt to use the admin menus for 2nd site fail and is routed to the redirection url.
I have 3 hosting beta test sites and they ALL fail in this way. So you can reproduce this in a heart beat.
Using 2 domains set and verified in hosting domain admin
Set masking url and 404 redirection
Try to go to 2nd domain site from network admin menu
If I go directly to the domain.tld/maskedurl login it allows me to logon.
Any attempt to use menu in admin area to change sites fails.
Logon to the 2nd site and you can't go to the 1st site and vise versa.