TriggerRegisterForItems(trigger) worked for me.

Are you starting with the item already inside the trigger? Or is the player moving the item inside the trigger? I was doing the second one.

My D:OS Mods:
Dunamis - A 15 hour Adventure Mod for D:OS EE

A Necromancer's Crusade - 10 hour adventure mod for D:OS EE

4 Character Creation (EE)