@MrJunior said:
As I can see the cpanel not allowing me to create subdomain like:sub2.sub.example.com. But I’m able to create sub of a sub to a ‘domain’example.rf.gd. Why can’t it be possible with regular subdomains of top-level domain?
Being able to create subdomains of subdomains is officially not supposed to be possible. The fact that you can do so now for some (free) subdomains is a bug already. Sub-subdomains are supposed to be a premium only feature.