Call post method api using http request in android studio

public String CreateOrder(String strAmt){


       String strRtn = "";

       try {

           final String POST_PARAMS = "{\n" + "\"amount\": \""+strAmt+"\",\r\n" + "\"currency\": \"INR\",\r\n" + "}";

           System.out.println("################ " + POST_PARAMS);
           String spec = "https://api.razorpay.com/v1/orders";
           URL obj = new URL(spec);
           HttpURLConnection postConnection = (HttpURLConnection) obj.openConnection();
          postConnection.setRequestMethod("POST");

           postConnection.setRequestProperty("username", "rzp_test_ABC");
           postConnection.setRequestProperty("password", "234324324324");
           postConnection.setRequestProperty("Content-Type", "application/json");
           postConnection.setDoOutput(true);

           OutputStream os = postConnection.getOutputStream();
           os.write(POST_PARAMS.getBytes());
           os.flush();
           os.close();

           int responseCode = postConnection.getResponseCode();


           InputStream in = new BufferedInputStream(postConnection.getInputStream());
           BufferedReader reader = new BufferedReader(new InputStreamReader(in));
           StringBuilder result = new StringBuilder();
           String line;
           while ((line = reader.readLine()) != null) {
               result.append(line);
           }
           strRtn= result.toString();


       }
       catch (Exception ex) {
           strRtn = "ERROR IN RAZOPay API : " + ex.toString();
           ex.printStackTrace();
       }
       return strRtn;
   }