Most hosted discourse instances are on a subdomain:
This is our general recommendation in almost all cases, and it works great. However, if you wish to use a root domain or apex domain for your hosted discourse, like so
this turns out to be surprisingly difficult in a hosting scenario, due to the vagaries of how DNS works.
It is possible, however, you must use a DNS provider that specifically supports it! Here is a list of known-compatible DNS providers, and the name of the DNS type that you should use:
So if your DNS provider is not one of these, you must switch to one of these DNS providers to achieve an apex domain or root domain hosted discourse.