The clicking noise will be the latch trying to unlock. Sounds like you have a sticking or faulty latch mechanism. There are two parts to the electronic tailgate the powered rams that lift the tailgate up and down and the latch which secures the tailgate in place.
If you can pop it from the inside and the tailgate moves up and down then I suggest the mechanism for raising and lowering the tailgate is working fine and the fault is in the latch mechanism (in the middle of the tailgate and or the lower trim in the middle of the boot itself.
Once popped open make sure there’s nothing stuck in the latch itself and possibly try something to free it off if its stuck.