If you believe that subdomain has been correctly added, determine if the created subdomain is resolving to server IP address. Run following commands from Windows command prompt/Linux terminal.
Above web diagnosis tools will tell you if created subdomain is correctly resolving to web server's IP address. If not, you should check with DNS zone of the subdomain. Go to DNS zone of your subdomain and determine if it has an appropriate A records with correct IP address.
If your subdomain still does not work, you can contact our support team at any time.