@chengnay as a test I set up a new project with the same Unity version, with VIU and SteamVR updated to the most recent versions, and everything but the pad was detected.
I used the following to check if it was triggered:
var state = ViveInput.GetState(TrackerRole.Tracker1);
print(state.LastPressDownTime(ControllerButton.Grip) + " " + state.LastPressDownTime(ControllerButton.Trigger) + " " + state.PreviousButtonPressed + " " + state.CurrentButtonPressed);
print(state.GetPadAxis() + " " + state.GetAxis(ControllerAxis.PadX) + " " + state.GetAxis(ControllerAxis.PadY) + " " + state.PadPressAxis + " " + state.PadTouchAxis);
if (ViveInput.GetPressEx(TrackerRole.Tracker1, ControllerButton.Pad))
Debug.Log("Pad Pressed");
if (ViveInput.GetPressEx(TrackerRole.Tracker1, ControllerButton.Trigger))
Debug.Log("Trigger Pressed");
Of these, I was able to get nonzero values of LastPressDownTime for Trigger and Grip, was able to see the PreviousButtonPressed and CurrentButtonPressed change with non-pad inputs, and saw "Trigger Pressed" when those pins were connected.