HTTP Error Code 415 - JSON arrays in JAVA

Question

I am trying to produce and send via JAVA a JSON file and when I am trying to add a nested object with an array in order to fit an application's protocol (which is not important to the question) the java program cannot send the file because of an HTTP error, code 415 (unsupported media type), which is strange because the produced JSON works when I copy it in the destined application (Google's DialogFlow). In other words, JSON is functional but JAVA (version 1.8) does not recognize it. Does anyone have any ideas why that happens?

When the part with the JSONArray in not included in the JSON file the request is sent without problem (see code below). I have tried changing the content-type from "application/json;charset=utf8" to "application/json;charset=utf-8" or "application/json" but nothing worked (this part in not included in the code because the changes that resulted in JSON not working were in the block below).

Part not working:

 static JSONObject messageToJSON()
 {
 JSONObject requestJson = new JSONObject();
 JSONObject meta= new JSONObject();
 JSONObject payload= new JSONObject();
 JSONArray arrayJson = new JSONArray();
 String messageData="My Message";    
 try
 {
 requestJson.put("message", messageData);
 requestJson.put("messageType", "html");
 payload.put("title",  "Thanks");
 payload.put("message",  "Thank you");
 arrayJson.put(payload);
 meta.put("contentType", "300");
 meta.put("templateId", "6");
 meta.put("contentType", "300");
 meta.put("payload", arrayJson);
 requestJson.put("metadata", meta);
 System.out.println(requestJson.toString());
 }
 catch (JSONException e)
 {
 e.printStackTrace();
 }
 return requestJson;
 }

The part working (without the extra layer in JSON, e.g. the payload JSON object and the arrayJson JSON array):

 static JSONObject messageToJSON()
 {
 JSONObject requestJson = new JSONObject();
 JSONObject meta= new JSONObject();
 JSONObject payload= new JSONObject();
 JSONArray arrayJson = new JSONArray();
 String messageData="My Message";    
 try
 {
 requestJson.put("message", messageData);
 requestJson.put("messageType", "html");
 meta.put("contentType", "300");
 meta.put("templateId", "6");
 meta.put("contentType", "300");
 requestJson.put("metadata", meta);
 System.out.println(requestJson.toString());
 }
 catch (JSONException e)
 {
 e.printStackTrace();
 }  
 return requestJson;
 }

Answer 1

Ok, I found the problem. I should have transformed the arrayJson from JSONArray type to string. In other words, instead of

meta.put("payload", arrayJson);

I should have

meta.put("payload", arrayJson.toString());

or make the arrayJson in a string format from the beginning.