Some error occurred message in payUmoney integration after generating successfully Hashkey

I was trying to integrate payment gateway of payUmoney. I was following this method Hash key was successfully generated but still i am not able to go to payment page using live credential. I am using this Code for generating the HashKey--

<?php
/**
 * Created by PhpStorm.
 * User: Mayur Dusane
 * Date: 21-12-2017
 * Time: 11:27
 */
/**************
Below is the test card details for doing a test transaction in the testing mode.
Card No - 5123456789012346
Expiry - 05/2020
CVV - 123
****************/
/***************** NECESSARY FIELDS GOES HERE ***********************/
$key=$_POST["key"]; //posted merchant key from client
$salt="e5iIg1jwi8"; // add salt here from your credentials in payUMoney dashboard
$txnId=$_POST["txnid"]; //posted txnid from client
$amount=$_POST["amount"]; //posted amount from client 
$productName=$_POST["productInfo"]; // posted product info from client
$firstName=$_POST["firstName"]; // posted firstname from and must be without space
$email=$_POST["email"]; // posted email from client
/***************** USER DEFINED VARIABLES GOES HERE ***********************/
//all varibles posted from client
$udf1=$_POST["udf1"];
$udf2=$_POST["udf2"];
$udf3=$_POST["udf3"];
$udf4=$_POST["udf4"];
$udf5=$_POST["udf5"];
/***************** DO NOT EDIT ***********************/
$payhash_str = $key . '|' . checkNull($txnId) . '|' .checkNull($amount)  . '|' .checkNull($productName)  . '|' . checkNull($firstName) . '|' . checkNull($email) . '|' . checkNull($udf1) . '|' . checkNull($udf2) . '|' . checkNull($udf3) . '|' . checkNull($udf4) . '|' . checkNull($udf5) . '||||||'. $salt;
function checkNull($value) {
            if ($value == null) {
                  return '';
            } else {
                  return $value;
            }
      }
$hash = strtolower(hash('sha512', $payhash_str));
/***************** DO NOT EDIT ***********************/
$arr['result'] = $hash;
$arr['status']=0;
$arr['errorCode']=null;
$arr['responseCode']=null;
$output=$arr;
echo json_encode($output);
?>

when i was sending this hash key generated from above code using this method:

  private class GetHashesFromServerTask extends AsyncTask<String, String, String> {
    private ProgressDialog progressDialog;

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        progressDialog = new ProgressDialog(MainActivity.this);
        progressDialog.setMessage("Please wait...");
        progressDialog.show();
    }

    @Override
    protected String doInBackground(String... postParams) {

        String merchantHash = "";
        try {
            //TODO Below url is just for testing purpose, merchant needs to replace this with their server side hash generation url
            URL url = new URL("https://payu.herokuapp.com/get_hash");

            String postParam = postParams[0];

            byte[] postParamsByte = postParam.getBytes("UTF-8");

            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("POST");
            conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
            conn.setRequestProperty("Content-Length", String.valueOf(postParamsByte.length));
            conn.setDoOutput(true);
            conn.getOutputStream().write(postParamsByte);

            InputStream responseInputStream = conn.getInputStream();
            StringBuffer responseStringBuffer = new StringBuffer();
            byte[] byteContainer = new byte[1024];
            for (int i; (i = responseInputStream.read(byteContainer)) != -1; ) {
                responseStringBuffer.append(new String(byteContainer, 0, i));
            }

            JSONObject response = new JSONObject(responseStringBuffer.toString());

            Iterator<String> payuHashIterator = response.keys();
            while (payuHashIterator.hasNext()) {
                String key = payuHashIterator.next();
                switch (key) {
                    /**
                     * This hash is mandatory and needs to be generated from merchant's server side
                     *
                     */
                    case "payment_hash":
                        merchantHash = response.getString(key);
                        break;
                    default:
                        break;
                }
            }

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (ProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return merchantHash;
    }

    @Override
    protected void onPostExecute(String merchantHash) {
        super.onPostExecute(merchantHash);

        progressDialog.dismiss();
        payNowButton.setEnabled(true);

        if (merchantHash.isEmpty() || merchantHash.equals("")) {
            Toast.makeText(MainActivity.this, "Could not generate hash", Toast.LENGTH_SHORT).show();
        } else {
            mPaymentParams.setMerchantHash(merchantHash);

            if (AppPreference.selectedTheme != -1) {
                PayUmoneyFlowManager.startPayUMoneyFlow(mPaymentParams, MainActivity.this, AppPreference.selectedTheme, mAppPreference.isOverrideResultScreen());
            } else {
                PayUmoneyFlowManager.startPayUMoneyFlow(mPaymentParams, MainActivity.this, R.style.AppTheme_default, mAppPreference.isOverrideResultScreen());
            }
        }
    }
}

Is the code is ok for generating hash key
Thanks in Andvance

Make sure your keys which you are sending to the payUmoney gateway are same as defined in PHP script hash generation

for example: key for product name is productInfo make sure of each character is same.

else the code is perfect this is only where you might have mistaken