Cpanel offers 15 day trials, some times even after you buy the license it keep showing the Trail license Message
Trial License This copy of cPanel
WHM is for trial use and will expire at the end of the trial period. You will need to upgrade to a paid
copy of cPanel & WHM to continue using the software after that period.
In such situation first you need to verify if your lincese has been activated by cPanel. to do that visit http://verify.cpanel.net and enter your servers main IP. This must be the IP that server uses to make outbound connections. And if you find your license valid then run
/usr/local/cpanel/cpkeyclt
from SSH. It will update the license at server.
Updating cPanel license...Done. Update succeeded.
Building global cache for cpanel...Done
If you have a valid license and you wish to install it on some other, you will need to email to cPanel support and they will change the IP for you.