What version are you using? 3.15 or 3.16? (3.16 was released just yesterday).

Do you get any kind of error when clicking it or when opening TPT? If you get one when opening TPT try to write it down and tell me what it says.

I've seen this once before and gave someone a fix where they had to move the tpt.register_mouseevent and evt.register lines at the very end of the script, up a little to near where the tpt.register_step is. I wonder if that's your problem, if so I should probably release a new update ...