Follow these steps and then try attempting the test again.

Step 1: Check if your camera is working properly by opening any of these websites

https://webcamtests.com/

https://www.onlinemictest.com/webcam-test/

Step 2: Make sure your device is connected to a single camera. Disconnect other camera devices before starting the exam (Having a built-in cam would be preferable).

Step 3: Check if any Antivirus Software/Extension is blocking the camera access. If yes, disable them.

Note: Using your personal Laptop/PC is better than a company/organization laptop.