The liveview does not work
Darkroom Booth | Documentation | Troubleshooting Guide
First, make sure your camera supports liveview. Many older SLR cameras will work with Booth but do not have the live view feature. Next, make sure the "Use liveview if supported by camera" option is checked in the live view tab. Click on the test button in the Live View tab and see if live view opens in the preview on that tab. If it does but is black see if the "exposure compensation" box is checked to the left of the Test button. Finally, make sure the camera is set to P, M, Tv, or Av mode, many of the other specialty settings disable live view.