Devido a RFC1738 a cPanel desabilitou a criação de subdomínios que iniciem com números.
Este regra é válida a partir da versão 11.25

Mensagem original:

Originally Posted by Jamyn Shanley

Hi,RFC1738 says subdomains cannot start with a number. The decision was made to follow RFC in this case. I realize this was not checked in cPanel v11.24.5, but it is currently checked for validity in 11.25. In short, the rejection of subdomains starting with a number is by design at this time due to rules in RFC1738. Thanks!
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Jamyn Shanley, Analyst
cPanel of Texas, Inc.