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The boxes were blocking the two Laser Receivers attached to the wall. By shrinking boxes, you let the lasers fall into the receivers, causing the door to respond to the gun. I can understand now that this was not obvious. I will add some visual cues (after the voting period is over) like visible lasers and adding a bulb over the door which will glow after the boxes are not obstructing the laser receivers or something like that. If you have any suggestions, kindly share them here.