As noted #44 is the trigger pin, the part around which the trigger pivots. It's held in the pistol by the slide stop spring and should never just "fall out" -- read as "someone removed this from the pistol."
This is a photo of my M92G but the KWA is the same. Pin inserts left to right.
I know for sure the real Beretta M92 trigger return spring works in the M9 PTP as there's one in my M9 PTP (from my efforts to increase the trigger weight). The Beretta trigger pin may also work but I've had no reason to try it. Brownells has the Beretta spring and pin if KWA does not.
Also note you'll need to properly install the slide stop spring to retain the trigger pin.