- Is another UI object covering it?
- Is you canvas/canvas group set to be interactable?
- Try removing all object apart from your button and one by one re-enable them
- Could Time.Time be set to 0? Unlikely but worth a shot!
- Double check if your button has acctually got an onClick event
this could be for many reasons, but an issue i had was that there was a ui element that was over my button