Before you start a test for the first time, you have to allow the Seamless Desktop Recorder to access your microphone and camera.
You may have accidentally blocked this access during setup. Review this article to learn how to reset these permissions so you can continue with your test.
How to reset permissions in Safari
Click Safari > Preferences.
Click the Websites tab, find the permission you'd like to reset (camera or microphone), and change the selection to Allow next to the UserTesting Recorder URL.