If you are the Agent who uses macOS to host a call session and encounter an issue where you see black video screen or the call is suddenly dropped when turning on the Camera, you can apply the following steps to fix the issue:
1. Logout / disconnect from console.sightcall.com. If you're connecting to SightCall from Salesforce, then you need to logout from Salesforce.
2. Go to mac System Preferences > Security and Privacy.
3. Under Camera, Microphone, and Screen Recording each, uncheck and re-check "SightCall" from the list.