You already have sent an email about this, October 10th, and you been replied to the next morning, with an email explaining what the problem might be:
If the “Add-on Manager” menu reports GSX as activated, then it is activated, no question about it. If you still see the Trial airports menu, the problem is likely you are mistakenly running P3D into a “Compatibility” mode, like XP Compatibility under Window 7 or similar.
Every Compatibility option for the Prepar3D.exe file must be turned off.
Also, be sure you don’t use other 3rd party add ons that starts with P3D that sets Compatibility mode, that might cause the same problem, and are also bad for performances.
But you never replied to it.
It's no use posting on the forum something you have been already supported with by email.