Volley send JSONObject to server with POST method

You can use the following working sample code. I have tested. Hope this helps!

       try {
            jsonBody = new JSONObject();
            jsonBody.put("Title", "VolleyApp Android Demo");
            jsonBody.put("Author", "BNK");
            jsonBody.put("Date", "2015/08/26");
            requestBody = jsonBody.toString();

            StringRequest stringRequest = new StringRequest(1, url, new Response.Listener<String>() {
                @Override
                public void onResponse(String response) {
                    textView.setText(response);
                }
            }, new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    textView.setText(error.toString());
                }
            }) {
                @Override
                public String getBodyContentType() {
                    return String.format("application/json; charset=utf-8");
                }

                @Override
                public byte[] getBody() throws AuthFailureError {
                    try {
                        return requestBody == null ? null : requestBody.getBytes("utf-8");
                    } catch (UnsupportedEncodingException uee) {
                        VolleyLog.wtf("Unsupported Encoding while trying to get the bytes of %s using %s",
                                requestBody, "utf-8");
                        return null;
                    }
                }
            };
            MySingleton.getInstance(this).addToRequestQueue(stringRequest);
        } catch (JSONException e) {
            e.printStackTrace();
        }

UPDATE: To create JSONObject as your requirement, use the following:

        JSONObject jsonObject = new JSONObject();
        try {
            jsonObject.put("11", 3);
            jsonObject.put("12", 4);
            jsonObject.put("13", 5);

            JSONObject jsonObject2 = new JSONObject().put("answers", jsonObject);
            jsonObject2.put("user_id", 12);            
        } catch (JSONException e) {
            e.printStackTrace();
        }