Render ONLY shadows cast on ground with shadow canvas

doibhil

I have a scene, someone walking with their shadow cast on the ground. I have no physical ground, just the iRAY ground (through the "draw ground" option). I have tried using the shadow canvas to render JUST their shadow on the ground (without the person), but the render always comes up blank. What am I doing wrong? I can find practically no resources online explaining how to use the shadow canvas. Can someone possibly provide a detailed step by step guide on how to do it? I also tried adding a physical plane primitive to catch the shadows, but that didn't work either. Thanks a lot in advance.