If you install Remote Desktop Services on the server, but you do not have any CAL Licenses on the service, you will receive an error for remote connection.
The Remote Desktop Service is for hosting your own RDP Service for groups of server typically, using AD.
To resolve, close any RDP sessions on your computer, then hit Windows Key + R to open a run prompt and input this; mstsc /admin
Then try to connect as per usual. That should ignore the RDS licensing service and let you connect. Once you connect, go into Server Manager and remove the Remote Desktop Services or purchase and install CAL Licenses for the service from Microsoft.