I've created pause/play button but it only works on one slide. If I put them on another slide it doesn't work.

Can you show a screenshot of the actions?

Why create a button that has to be inserted on each slide, instead of using a shape button on the master slides? Are you still on a very old version?

I'm asking this question for this reason: if the action you created is hiding/showing objects (to change the look of the toggle buttons), they point to those objects using their ID. When you copy/paste the objects to another slide, that ID will be different because it has to be unique. The advantage of a shape button, put on the first slide, and timed for the rest of the project (always on top) is that you have to deal only with one ID.