If GSX Pro reports as "Active" in the FSDT Installer, but is on Trial in the sim, the problem is likely your user account in Windows that has limited permission. You can try this solution:
- Go to this folder ( the folder the FSDT Installer is installed into, by default C:\Program Files (x86)\Addon Manager ) and look for this file:
\Addon Manager\Couatl64\Couatl64_MSFS.EXE
- Right-click on it, select "Properties", then "Compatibility" and check the "Run As Administrator" option.