A proper hostname must be set in order for license activation to work properly. This is usually done for you when your account is created but sometimes cPanel will still complain.
The next step involves updating the cPanel license file which must be done through the linux shell.
You can login to shell through SSH. We do not support telnet, only SSH because telnet traffic is not encrypted. A free Windows SSH client called PuTTy is available from the link below.
You will need to use port 22 to connect.
MacOS and Linux users can use command 'ssh root@YourprimaryIP' from the terminal
Once logged in you need to execute the following command, type it as follows:
/usr/local/cpanel/cpkeyclt
Now you should successfully be able to login to WHM without errors. Please submit a support ticket for further assistance with this issue.