If you have multiple cameras on your device, there is a chance that the platform will pick the first one in the hardware list, which may not be the one you want. If that’s the case, see if you can share a different camera in the “Allow” prompt.
When using the discuss.io meeting room, click on the “Camera” button in the URL bar and see if the desired camera appears in the Camera drop-down:
You can also decide which camera to use in your Device Settings, which appears after you complete the tech check. Your available cameras appear in a dropdown prior to joining a session.