Configure a license server for the terminal server. If you have an existing license server, use Terminal Services Configuration ...

Configure a license server for the terminal server. If you have an existing license server, use Terminal Services Configuration tool to specify that license server for the terminal server. Otherwise, install TS Licensing on a computer on your network.  If you have configured a license server for the terminal server but the license server does not appear in the list of discovered license servers, use TS Licensing Manager to review the configuration of the license server.