This may be an issue if you're accessing the workout from the Chrome browser due to Chrome's security permissions. If you denied access or may have skipped that step, you can still easily grant permission.

On the left side of the URL bar in Chrome, you'll see a circle icon with a dot and a line repeated twice. If you click on that, you'll see your options to grant access to your camera and microphone. You'll want to ensure they're both toggled on.