What happens when you run the command directly?
sudo docker exec container_name /usr/bin/mediacenter28 /RestoreFromFile license.mjr
Also make sure that the .mjr file is readable inside the container. You indicated that it activated successfully using the dialog, but I'm not sure if you meant inside the container or on your Windows machine.
The screen of JRMC28 turns to black and returns immediately (Looks like a MC shutdown and restart), but same result - not activated.
Even with /config/license.mjr does not activate.
sudo docker exec container_name /usr/bin/mediacenter28 /RestoreFromFile /config/license.mjr
The .mjr file is readable and writeable but not executable.
QNAP NAS: The activation works in the container when I enter the Registration Code in the 'Restore License" window.
Windows PC: As I don't know how to remove the present MC 28 license from my Windows installation.
I just double clicked the .mjr file and got an Information window 'License for Media Center was successfully installed!
But it still indicates theMC28 license.