Welcome to Unreal Forums!
Depending how you’re handling your interaction with the door, you would need to get your inventory component (inside your player character) → get the array that represents your inventory slots (items?), check if the item required by the door is in your inventory and if so check quantity is greater or equal to 4 (or whatever you need it to be). If yes, open door.
I don’t have an inventory that I could showcase right now with this, but if you are unable to get this working I could put something together, probably tomorrow.