I have a Google Sheets add-on published privately (only those with link can install) on domain 1 (G Suite Business).
I tested on domain 2 (G Suite Business) and it installed (although I get the unverified app message which is fine). No problem here.
I asked a friend to test on his domain which is a G Suite Education domain and it would not install, got an error message:
What setting does the Google domain admin (for Education) have to turn on to allow this add-on to install? Is this specific to Education domains?