Does it have to be a supported?

Does it have to be one of the supported cameras for the live view to work? I have a Pentax K50 and haven’t been able to get it to work

Yes, currently iStopMotion supports certain Nikon and Canon models. However, you may use the HDMI output of the camera with a HDMI grabber (e.g. https://www.epiphan.com/products/dvi2usb-3-0/ ) and capture this signal in iStopMotion. Not sure if you can switch off the overlays in the cameras output thought.