In Final Cut Pro I can't get the multicam function to work. Has anyone else experienced this?

Some more information may help us help you.

How is it that is not working? Some error message, an outcome that is not how you expected, what?

Are you selecting the clips in the browser, choosing New Multicam Clip, and then...

One common issue is that the clips may not end up in the Angles as expected. To this end, you should help FCP by filling in the Camera Angle or Camera Name metadata in the Inspector: select all the clips from the same camera, and give them the same value - say, "Camera A", and likewise for each of the angles.

A screenshot, as Tom suggested, may help.

When you say “not synchronous” - can you be more specific? Are they just misaligned, or are they all one after another in the same angle?

I'm sure someone has; ask here: https://discussions.apple.com/community/applications-services/final-cut-pro

No. What exactly happens? Post a screenshot of the multicam clip editor. Please give details of the specs of the media video and audio.