Stickup cam not registering motion

Our neighbour throws rubbish (rocks / rotten food / dead vermin) into our front yard over a 1.8 metre fence. SA police recommended video evidence before charges brought. I’ve set up Stickup gen3 battery cam at approximately 10 feet away from the fence - I’ve tuned the field of coverage, set maximum motion sensor, turned off smart alerts, turned on video recording of motion but it’s not working. I’ve conducted tests where I throw items (small box / rolled tea towels / apples) in front of the camera but nothing is captured, but if I wave a broom in front of the camera this is. Surely your camera should register when an object moves over field of view? Help me please because this has so far been a waste of time / money / effort.