Multisite installation check up

I just finish to install the multisite for the first time and I notice that I can't create a new site with a new domaine name.
I have 2 domaine name. is my main domaine. I bought the second one, few one week ago. Now I would like to create a site with that new domaine name...

As you can see on this screenshot, I look like all I can create is a sub-domaine. I'm not 100% sure if I done the installation well that why I would like to have some advice. Is there something wrong with my installation? What can I do to fixe this?

Thank for your help.


PS: I'm with Hostgator. I sent them a message about this they asked me to park the new domain, still, it didn't change anything. My website is