How to license Windows Server 2012 Remote Desktop Server (Terminal Server)

When you add a new RD Session Host to an existing environment and it doesn’t detect the license server:

 

https://social.technet.microsoft.com/Forums/windowsserver/en-US/8c310258-18ff-4cd4-bab0-52796a5dd9b2/remote-desktop-session-host-server-is-within-its-grace-period-but-the-rd-session-host-server-has