Java/Android: Backslashes in JSON in Double Quotation places - json

Question

I try to send "POST" request to serwer. Request includes JSON. Server returns "ok" or my JSON (in value of "message" key), if data in not correct. And I get strange backslashes ( \ sing) in my JSON, sent to server.
I get JSON response:
{"message":{"{\"phone_number\":\"_380661111111\",\"password\":\"112233aa\",\"military_id\":\"12345\",\"email\":\"won#mail_ru\"}":""}}
Normal JSON:
{"phone_number":"380666320670","password":"112233aa","military_id":"12345","email":"wovilon#mail.ru"}
Full code:
class SendLoginData extends AsyncTask<Void, Void, Void> {
String[] key,value;
String mResultString;
SendLoginData(String[] inKey, String[] inValue ){
this.key=new String[inKey.length];
this.value=new String[inValue.length];
this.key=inKey;
this.value=inValue;
}
String resultString = null;
#Override
protected void onPreExecute() {
super.onPreExecute();
}
#Override
protected Void doInBackground(Void... params) {
try {// http://oasushqg.beget.tech/users
String myURL = "http://y937220i.bget.ru/users";
byte[] data = null;
InputStream is = null;
try {
URL url = new URL(myURL);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("POST");
conn.setDoOutput(true);
conn.setDoInput(true);
OutputStream os = conn.getOutputStream();
//Create JSONObject here
JSONObject jsonParam = new JSONObject();
for (int i=0; i<this.key.length; i++) {
jsonParam.put(this.key[i], this.value[i]);
}
data=jsonParam.toString().getBytes("UTF-8");
os.write(data);
Log.d("MyLOG", "data is next: "+new String(data, "UTF-8"));
data = null;
conn.connect();
int responseCode= conn.getResponseCode();
ByteArrayOutputStream baos = new ByteArrayOutputStream();
if (responseCode == 200) {
is = conn.getInputStream();
byte[] buffer = new byte[8192]; // Такого вот размера буфер
// Далее, например, вот так читаем ответ
int bytesRead;
while ((bytesRead = is.read(buffer)) != -1) {
baos.write(buffer, 0, bytesRead);
}
data = baos.toByteArray();
resultString = new String(data, "UTF-8");
JSONObject jsonObj=new JSONObject(resultString);
mResultString=jsonObj.getString("message");
} else {
}
} catch (MalformedURLException e) {
} catch (IOException e) {
} catch (Exception e) {
}
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
#Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
if(resultString != null) {
Log.d("MyLOG", "postExecute run");
Log.d("MyLOG", mResultString);
}
}}