Using a Campark ACT74 action cam as a webcam in macOS 10.12 I recently got a Campark ACT74 action cam, with the intention of using it as a camera with which to live-stream stuff to Twitch and the like. Upon plugging it in to my Macbook Pro (2015, 10.12) --- nothing happens. It doesn't appear in OBS, PhotoBooth or QuickTime, despite selecting the "PC Camera" option when prompted by the camera upon plugging it in. I tried getting it to work with the open-source "macam" software, but that didn't recognize it either.

How can I make this camera work with macOS?
According to the User Manual available here this actioncam cannot be used as a webcam. The prompt you get upon connecting the device via USB lets you probably choose between Mass Storage (UMS) Protocol and Camera (usually abbreviated PTP - Picture Transfer Protocol). 

Both protocols let you transfer pictures from the actioncam to your Mac/PC but neither of those allows the camera to be used as a webcam. That's the reason why it will not show up in any of the mentioned applications in your question.

However, if you have a HDMI capture card or a device to capture HDMI input, you could theoretically capture the output of the actioncam using the HDMI output of the camera on the side. If you don't have such a card you are probably better off just buying a webcam supported by macOS since those HDMI capture cards are more expensive than a webcam.