wh987456 cloudns.be is a public domain name; someone has bound the cloudns.be domain name to the server, preventing other users from binding the cloudns.be subdomain to the server.
wh987456 This is the public suffix list https://publicsuffix.org/list/public_suffix_list.dat. Administrators should set up a blacklist to prevent anyone from binding the root domains in the list, only allowing the binding of subdomains under the root domains.