The most common easy-to-fix problem on the Mac, is that the webcam is not selected as the correct broadcasting device.
How to fix:
1. In a Vyew meeting, Control-Click (right-click) on the screen and select SETTINGS.
2. Select the CAMERA tab (lower right tab)
3. Look at the DEVICE dropdown and choose “USB Video Class” (or something similar)
If that doesnt work, try other devices from the drop down menu.
If it still doesnt work, post to this thread.