Can't get "Item Mapping" in the output of custom action in integration

I am trying to create an integration receipt with custom action and found a problem with output.
My receipt contains a build-in trigger “When column changes”, docs here
I also created a custom action with fields that are described in trigger’s docs:

When I use this integration, I get results with all fields except “itemMaping”. That is the POST request that my application got, there is no “ItemValues” here:

Please help, why this happens? Also I’ve tried to do the same with build-in trigger “When Button Clicked” but got the same results.

Also I’ve found another topic with the same question, but there is no answer: