Create JSONObject inside JSONObject to post the data

I would like to create below JSON for the post in the body. I would like to build this JSON using the native class.

[
  {
    "message": {
      "data": "E-Stop Off"
    },
    "platform": "ros",
    "topic": "/android_app/nav_control",
    "type": "std_msgs/String",
    "expiration_secs": 1
    
  }
]

I am using this method more often with few changes that is why I pass the argument in the method. I am not able to add JSONObject inside JSONObject. Here is my effort.

 public String postCommandJSON(JSONObject jsonObject, String topic, String type) {

        JSONArray jsonArray = new JSONArray();
        try {
            JSONObject mainObject = new JSONObject();

            mainObject.put("platform", "ros");
            mainObject.put("topic", topic);
            mainObject.put("type", type);
            mainObject.put("expiration_secs", 1);

            mainObject.put(jsonObject);
            jsonArray.put(mainObject);
        } catch (JSONException e) {
            e.printStackTrace();
        }
        
        return jsonArray.toString();
    }

I am not able to add JSONObject inside JSONObject in below line.

> mainObject.put(jsonObject);

Thank you

Assuming that at mainObject.put(jsonObject); you attempt to crate something along

{
    "message": {
      "data": "E-Stop Off"
    }
    ...
}

then beside value (which will be JSON object) you also need to pass to put method a key via which we will later be able to access that value.

So you probably want to change that line into

mainObject.put("message", jsonObject);

and maybe even execute it before mainObject.put("platform", "ros"); if order of elements is important.