Diagnosis.
CHECK IT EXISTS IN CPANEL
Domains should list it with a document root.
CHECK WHERE YOUR DNS IS
If your nameservers point elsewhere, cPanel creating a subdomain does not make it resolve.
An A record must exist at your actual DNS provider.
That is the most common cause.
CHECK THE DNS RECORD
Look up the subdomain. Does it return your server's address?
CHECK THE SPELLING
A typographical error in the subdomain name.
CHECK PROPAGATION
A newly created record may take a short time.
CHECK FOR A CONFLICTING RECORD
A wildcard record may be answering instead, sending it somewhere unexpected.
IF IT RESOLVES BUT SHOWS A CERTIFICATE WARNING
Run AutoSSL, ticking the subdomain.
IF IT RESOLVES BUT SHOWS THE WRONG CONTENT
Check the document root.
WHAT TO SEND US
The subdomain, what it resolves to, and where your DNS is hosted.
