To answer you question: no, you cannot host this domain name with us.
The domain qzz.io is actually listed in the Public Suffix List, but as a “Private Domain”. Meaning it’s not a real domain extension, just a domain used for free subdomains.
The client area got it wrong here in that it incorrectly detected your qzz.io subdomain as a valid domain name while it actually isn’t. The hosting platform itself is correctly blocking it.
A fix is being deployed for the client area to correct this.
This domain is effectively a third party free subdomain, and we do not support hosting subdomains from others here. You can either host your own domain name with us, or use one of our free subdomains.