The switch triggers with your finger, but not the ball, indicating the switch is out of adjustment. Verify the switch is firmly in place - no loose screws, etc.
You need to bend the actuator up so the ball will push down the switch arm further. It will not take much adjusting. Use a pair of needle nose pliers and bend near the switch. Ideally, you would have a tool for this, but pliers will do.
Do just a little at a time - its easy to wreck a switch if you aren't careful.