windows 2016 server RDP configuration
If you created a RDS deployment using Server Manager -- Add roles and features -- RDS install -- Quick/Standard -- Session-based you would set the licensing mode and RD Licensing server name in RDS Deployment Properties and make sure the server is part of a session collection.
If you do not create a RDS deployment then you can set it via group policy settings.
Computer Configuration\ Administrative Templates\ Windows Components\ Remote Desktop Services\ Remote Desktop Session Host\ Licensing
Use the specified Remote Desktop license servers Enabled and write License server to use
Set the Remote Desktop licensing mode Enabled and specify the licensing mode for the RD Session Host server Per User or Per Device