We have a hardware adapter with a single button the connects to the pogo pins.
I have a very simple unity secene that has a basic XR Origin and a GameObject for the tracker with a TrackedPose driver and a custom script with InputActionReference triggerReference = null; and callbacks ( triggerReference.action.started += TriggerCB; triggerReference.action.canceled += TriggerCB;) to detect the actions.
Did you add the HTC Tracker profile to the Interaction profiles and created a XR Input action map to associate the pose and trigger with the InputActionReference?