Advancing slides in PowerPoint

I am presenting live in front of an audience and over Zoom. When I share a PowerPoint presentation in full screen on the second monitor, I cannot get the clicker to advance the slides. The clicker WILL control the computers volume and escape from the presentation. When NOT in a Zoom meeting, the clicker works just fine. It is NOT simply a matter of which program has focus. With the mouse, I click on the slide advance arrows and the slide changes. I then immediately try the clicker; no good.