I’ve wasted about a week trying to figure this out, so cross posting to make it easier for anyone else to find that runs into the problem.
If you’ve enabled the overlay, plugged in the camera, and the board doesn’t boot then this post is for you. 
There is at least one batch of Radxa Zero 3W in circulation with an inverted MIPI CSI camera connector clip. The result is that you will inadvertently plug the camera in upside down, which is bad. Solution is to ask for an exchange, or try to flip the black part upside down. Zero 3W Camera 8M doesn’t work
The attached picture is what I guess the connector and cable is supposed to look like, and when I reverse the black clip and plug in the cable this way everything works.
