The first time you join a Call.Group meeting room via the Internet you may need to permit access to your device's microphone, camera and screen (for screen-sharing).
You should see a pop-up like those below. Simply click on 'Allow' when prompted.
If you don't see the options above, click on the padlock icon towards the top left of your browser window, then click on 'site settings' (or 'site permissions').
You'll then see a list of permissions for the Call.Group website and you can set microphone and camera access to 'Allow'.
If you're having difficulty with microphone, camera and screen access you may need to check that you are not blocking microphone, camera and screen access on your computer itself: