If you still have the original top case, look at the area where the power button is supposed to go. In the middle area where the bottom of the TouchID button rests there should be a small circular silvery piece of metal embedded in the top case. Now look at the same area on the replacement top case. Is the metal there or is it absent? If it's absent, you'll need to transfer over that little circular metal piece from the original top case to the new top case in order for the TouchID button to click properly. The easiest way to do that is by prying it up with fine nosed metal tweezers, and then laying it in place on the new top case (it's held in place by a little bit of adhesive). Good luck!