Pleased you have got it sortedπ - Ive just been through all of this with mine, it was getting harder and harder to open untill it completely stopped opening at the switch. I took off the rear panel and changed the micro switch, also the lock actuator but still no joy.
Ended up going to my local garage for advice - Mark fitted a solenoid onto the tailgate lock with a remote control box fitted in the engine bay for me.
I now have two fobs (original fob and tailgate fob) The tailgate is opening fine now with the new fob.