First try returning to your invitation and copying and pasting your link directly into your browser.  Sometimes there are issues with app interactions when you click through directly from an email app.  You can also try the following. You may not have enabled your camera.  You should see a pop up somewhere that asks for permission to access camera or audio.  Check your pop up blocker to see if it has blocked the pop up. Check whether another app is using your camera. Apps like Skype or Hangouts can sometimes retain control of your camera and microphone even after you have completed your session on them.   You can access permissions by clicking on the little icon to the left of the URL and allowing camera directly.  Also you can try closing all apps and restarting your device.