Yes it does must it need to be a stand alone subdomain. My error was that I first created a subdomain under my main domain, and it did not show in the domain list when trying to install via Installatron. But when I created the same subdomain as a stand alone domain it show up.
BUT, I forgot to delete the first subdomain so even if Installtron installed correctly I had a browser problem as I now had 2 subdomain with the same name.
After discovered that, and deleted the subdomain under the main domain it works just fine.
Thanks for all tips and help.
Bo