I am not good at tracking down json formatting issues but when I did have to play around in there I found this site very helpful in validating json info.
Also - with a little hunting around, there is this community post here that really gets some more detail about json - in particular in your code above , I don’t think you need to create a map, you can set_fields(json) directly based on what they are saying. Alternatively you can use select_jsonpath() to pull things specifically…
hope that helps…