Can't map a domain to a subsite set in multidomain

Hello dear support staff.

I’m creating a multisite network on

My issue is that after adding another domain ( as selectable in the multidomain, tried to map the same domain to but I can’t.

The error I get is that ( it is an invalid domain.

Is there some way to use the same domain as multidomain and map it to a subsite?

Thank you for your help!