You want to create a subdomain in the account that has the same domain as your server hostname. And you are doing the regular work that you always do when creating a subdomain. However, you get this error message.

This happens because the subdomain you want to add is a subdomain of the domain in the server’s hostname.

Please follow the below steps inorder to solve the issue.

1) Log into WHM and go to Home »Server Configuration »Tweak Settings.

2) Then locate the following option: “Allow users to park subdomains of the server’s hostname”

3) Set it to on and click on Save.

4) After enabling try to create again.