Coadmin privileges

I am trying to give coadmin privileges, but I keep receiving an error that both primary and secondary emails have to have verified domains.

The coadmin has only primary email and the domain (www.fiscoerevisione,it)  is included in the list of verified domains in Enterprise Settings.

My email domain (www.revisori.it) is verified too.

What's going wrong? Where is the mistake?

Thanks for your help