How do I register this properly?

[Tyrion101]

I found something called "Add on manager" and managed to supposedly register it, but I still keep getting the trial window on the menu screen. How do I register this the correct way?

[virtuali]

If you see the Trial airports menu, it means GSX is not activated so, check in the Addon Manager first, and see if the Addon Manager reports it as "In Trial" or "Active"

If the Addon Manager says it's in Trial, you only need to activate it.

If the Addon Manager says it's Active, then it's Active so, it's possible you are mistakenly running FSX or another addon that starts with or launches FSX, in "Compatibility mode", like XP mode under Windows 7 or similar.

Check you don't run FSX into a “Compatibility” mode, like XP or Vista or Windows 7, under Windows 8. Turn off any compatibility modes for the FSX.EXE, which is how FSX is installed by default.