Are you represented as a blank window in JackTrip, instead of it showing a video feed from your camera?
Initial troubleshooting
Sometimes just clicking the video button twice will help work-around whatever problem you are encountering. Click it once to disable, and then again to re-enable your camera.
If that doesn't work, try leaving the session and re-joining.
Windows only allows one application to access your camera at a time. If you are running on Windows and see the problem again after re-joining, try closing all your other applications and restarting JackTrip. If you are using a web browser to connect, close any other tabs that may be using your camera.
Make sure JackTrip has permission
Problems with video are most often caused by camera permissions settings in your computer's operating system. Please review one of these guides to ensure that JackTrip is granted access to your camera:
If you are using the Desktop App, please make sure that "JackTrip" has access to your camera.
If you are using a web browser, please make sure that your browser has access to your camera. In addition, you may need to review your browser settings to allow JackTrip's web application to access your camera.