If you are on a desktop, please check if you computer has a working camera and mic connected to it, most laptops and phones come with integrated cameras and microphones. Our pages have a setup screen where you can see whether the camera and mic is working or not.
The first image shows the setup screen where you can give the camera permission, next you can see a preview of the camera feed and the mic also has a loudness detector to indicate whether the mic is working or not.
Your camera might also being used by other applications installed on your computer, please close them and try again. The camera might also become stuck, if the page shows a "Cam/Mic not accessible" error a restart of the device usually fixes it.