Can I add a domain to my hosted panel domain?

[joximu]

ispcp runs as VirtualHost in Apache (the default VirtualHost), and the customer domains also are running as VirtualHosts - but you cannot run the same VirtualHost-Name two times - there's only one which comes to the browser...

So it's best not to use the domainname (alone) for ispcp - always add at least a host part (controlpanel.domain.tld or something like this) during setup...
It's possible to change the URL for ispcp - then you can add the domain to the users list.

/J