So, let me see if I understand. First of all the power switch must be OFF. If I remember well, the power switch has three positions: OFF, ACC (in Italian, I do not know in English) and ON. I wonder if it would work in the middle position too. Second, I have not to press the buttons (on key or close to dash) but to keep it pushed for several seconds. Is that correct?
The best way to learn it is to try it. Kind of like riding a bike or performing surgery.
Your car can be running in Park but must be unlocked for the dash button to work. Then it is
push and hold until the power liftgate operates. A quick press won't do it and it won't work if the car is locked. When the liftgate is moving, a quick press of the dash button will stop it. Another
push and hold will reverse the movement.
If the car is off, the keyfob
push and hold will work from outside even if locked. The manual liftback switch will work if the car is locked and the person has the keyfob.
If your car has a foot operated liftgate the car has to be off for that feature to work.
There are separate configurations for auto lock unlock. I use the auto lock unlock based on going into and out of Park. So anytime its in Park it will be unlocked.
Again some of this varies by your setup. Try it.