Adding a new site on sub-domain

Application Performance Getting Started
1

What is the name of the domain?

something.example.com

What is the issue you’re encountering

Only root domains allowed

What steps have you taken to resolve the issue?

Why wouldn’t it be possible to add a website that is on a sub-domain?
If the sub-domain has it’s own DNS zone that can be controlled by Cloudflare, that should make it technically possible to do anything required?

2

To be able to add the subdomain, it’s parent/suffix must be on the Public Suffix list: https://publicsuffix.org/list/public_suffix_list.dat

Other than that, the subdomain could be set up as a Partial (CNAME) zone, but this requires a Business or Enterprise plan: