As with many applications, WebEx needs access granted to the camera on a Mac.
Procedures or Details
On your Mac, choose Apple menu > System Preferences, click Security & Privacy, then click Privacy.
Select the checkbox next to an app to allow it to access your camera.
Deselect the checkbox to turn off access for that app.
If you turn off access for an app, you’re asked to turn it on again the next time that app tries to use your camera.