If you are using the Safari browser on your macOS device and our user testing tool has trouble accessing your Screen Sharing functionality then this could be because you've disabled access to it in your browser settings.
Click the `Safari` icon in your dock and click the `Safari` menu in the top left corner of your screen. Select `Preferences...`
Now make sure you have your user test open and click the `Websites` tab. Select `Screen Sharing` in the sidebar and make sure `marvelapp.com` is set to `Ask`.