Before joining a live interview, you need to allow your web browser to access your laptop camera. Here are the instructions on how to do that for Chrome/Firefox/Safari.
In the Chrome browser, a pop-up will open in the upper left corner. There you just have to click on "Allow".
Firefox also opens a pop-up. There you have to click on "Allow" to grant access to the web browser.
With the Safari browser, a central pop-up opens. By clicking on "Allow", you allow the browser access to the laptop camera.