I'm having difficulty using setItem to modify a JSON in a text field with a button.

I have a text field called json. It has a simple json object which is created with another button.

button code:
let newjson := {
        S: 1
    };
json := formatJSON(newjson)

What shows up in json text field:
{"S":1}

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In my modify button I have:

let getJson := parseJSON(json);
setItem(getJson, "S", "new");
json := formatJSON(getJson)

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All it does is empty out the field.

If I don't parseJSON() it crashes my DB.

What am I doing wrong?