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

Hello dear support staff.
I'm creating a multisite network on http://www.bloserver.com
My issue is that after adding another domain (http://www.miraiserver.com) as selectable in the multidomain, tried to map the same domain to http://www.bloserver.com/miraiserver-home but I can't.

The error I get is that (miraiserver.com) 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!

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