As in my knowledge, using subdomains should be seamless. Maybe because of that you don't need IP, but I'm not sure.
I know that this is not your case, but I've recently learned that to use a root domain as primary domain, you need to have CNAME Flattening ability on your DNS provider and sadly GoDaddy does not have that ability so one of my clients decided to use www as their primary domain to keep GoDaddy as their DNS manager. I've shared this because maybe it's related somehow.
Following link might help: