No Option for Add-On Domain

Thanks, I previously read the support article on Ad-On Domains vs Parked Domains. It states that “Parked Domains mean that both domains both serve content from the same directory.” I don’t want both of my domains pointing to the same content. Instead, I want my additional domain using a different directory that I can specify. (It is fine under my existing htdocs as long as the additional domain can get its own unique folder within the htdocs).

But, the issue seems to be that when I added the new domain ( the tool did not give me an option for the Add-On type. It only gave me choices of Parked or Subdomain. I’ve already tried deleting the new domain and adding it again, but it does not give me the option for “Add-On” that I need. Any ideas?