Cryptomatte Pick isn't working. What have I forgotten? Blender 2.81, 2.81a
Windows 10, 2xGTX1080 GPUs, GPU rendering

I've been through the Manual and a few tutorials, but I guess I'm missing something. Why can't I get the Cryptomatte Pick working? Is there another undocumented type of Pass that needs to be activated?

The scene is just the cube. I render the scene, hook up the nodes as below. I've tried both Object and Material options. Tips?
for me its working pretty good. using this since blender beta.
few tips to find out..

1- try this sample file
in my case, it looks like this. 

steps i did to check


create objects 
assign materials 
switch to cycles 
turn on cryptomatte (as you have already done ) 
hit render 
use cryptomatte nodes in compositor, tested via object and material both.