Hi rodpod_1,
Thank you for using the Apple Support Communities! I understand your built-in camera is not working for a specific program. I'd like to help.
It sounds like you did a good job checking System Preferences > Security & Privacy > Privacy > Camera, to see if this application is listed as an app that is allowed access to the camera: Control access to your camera on Mac - Apple Support. However, you mentioned you do not even see this program listed here. Is it possible that you are opening a meeting via the web browser instead or the app you may have installed?
I also found some helpful articles from the Manufacturer of this program directly, that appear to share guidance that could resolve your issue. Check out the articles here: GoToMeeting Attendee Guide for Mac, and Why don't I see the webcams option?. Do you have the latest version of the program installed? Download GoToWebinar Now.
Best regards.