Thanks, but how can a subdomain be added as a primary domain for an entirely different application? This would imply that the DNS of a main domain (www.OURDOMAIN.com or OURDOMAIN.com) is an absolutely useless concept. You can’t register a subdomain of a primary domain that is already registered, or else a domain would be meaningless. I can just register social.facebook.com on netlify and start a new website to compete with facebook.com? Obviously, that’s impossible.
The idea of any subdomain is that it is managed via the DNS of the main domain, via. a CNAME or A Record on the main domain pointing to the subdomain application. So only someone with access to the DNS of a main domain can manage subdomains of the main domain. If you try to add a subdomain as a primary domain on another application, you are trying to manage the DNS of the main domain via the DNS of a subdomain and this is not allowed for obvious reasons, as pointed out above.
As an aside, the way subdomains worked when we hosted our own DNS is quite simple:
Step 1: We added a C record on the primary domain for the subdomain and the value of the C record was the URL or IP of the server where the application for the subdomain resided.
Step 2: Then on the server where we hosted the other application, a DNS entry was added to make the server recognize requests from the subdomain URL.
The problem with Netlify DNS is that Step 1 is easy to do, but Step 2 is seemingly not available, as there is seemingly no way to point any “website.netlify.app” to anything other than a primary domain that requires registration, and since you can’t register a subdomain as a separate website, from the primary domain, how is this managed?