Hello there,
In "Per Device" licensing mode, you need to install the appropriate number of Client Access Licenses (CALs) on the license server for the number of devices that will connect to the RDSH server.
Access the licensing server and install the necessary "Per Device" CALs. Make sure that the CALs are valid and match the version of the RDSH server.
Similar discussion with an accepted answer here https://learn.microsoft.com/en-us/answers/questions/686010/the-remote-desktop-session-host-server-is-in-per-u
Hope this resolves your Query !!
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