Paid or not, won't make any difference at an FSDT airport, since the program would work exactly the same even when not purchased.
What you are describing seems odd, pressing CTRL+F12 at KFJFK when not in a parking should always give you a menu with 2 options: "GSX Select parking facility", and "New York JFK Airport", which is the previous YouControl menu, to control the hangar doors.
If you press it on a parking spot with Parking Brakes on and engines off, you should see "GSX - Activate ground services" and again "New York JFK Airport". If you see just the hangar opening menu, without going from the previous choice, it's because you haven't set the Parking Brake but, a red warning + a sound will tell you this quite clearly.