Hello,
You should verify the versions of your Licensing server, CALs, and Session host.
Ideally, the version compatibility should follow this order: Licensing server ≥ CALs ≥ Session host. The setup will function most smoothly when all components are of the same version.
For instance, if you have a 2016 CAL, it will work seamlessly with a 2016 Licensing server and a 2016 Session host. It may also be compatible with a 2019 Licensing server and a 2012 Session host, although this configuration is less optimal.
You can follow this doc for more details: https://video2.skills-academy.com/en-us/windows-server/remote/remote-desktop-services/rds-client-access-license
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