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1. Please verify that the license server has a client access license (CAL) for each device that can connect to RDS.
2. Verify that the Remote Desktop Session Host server is configured to use the correct licensing mode.
3. Using RD Licensing Diagnoser buttoto test the connection to the license server and report any errors.
4. If you have recently changed the licensing mode or added a new license server, you may need to restart the Remote Desktop Services on the RDSH server to apply the changes.