Paytm refund api gives 501 - System error in response - php

Question

I am using paytm refund api in php.
here is my code:
$checkSum = "";
$paramList = array();
// Create an array having all required parameters for creating checksum.
$paramList["MID"] = '**********';
$paramList["ORDERID"] = '*******'; //get during paytm transaction response
$paramList["TXNTYPE"] = 'REFUND';
$paramList["REFUNDAMOUNT"] = '50';
$paramList["TXNID"] = '***********'; // get during paytm transaction response
$paramList["REFID"] = 'REFID'.time();
//Here checksum string will return by getChecksumFromArray() function.
$checkSum = getRefundChecksumFromArray($paramList,PAYTM_MERCHANT_KEY);
$paramList["CHECKSUM"] = urlencode($checkSum);
$data_string = 'JsonData='.json_encode($paramList);
// initiate curl
$ch = curl_init();
$url = 'https://securegw-stage.paytm.in/refund/HANDLER_INTERNAL/REFUND';
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0);
curl_setopt($ch, CURLOPT_URL,$url);
curl_setopt($ch, CURLOPT_POST, true); // tell curl you want to post something
curl_setopt($ch, CURLOPT_POSTFIELDS,$data_string); // define what you want to post
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true); // return the output in string format
$headers = array();
$headers[] = 'Content-Type: application/json';
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
$output = curl_exec ($ch); // execute
$info = curl_getinfo($ch);
$data = json_decode($output, true);
print_r($data);
Here is the response, i am getting:
Array ( [RESPCODE] => 501 [RESPMSG] => System Error. [STATUS] => PENDING )
I am not getting that what this system error means. What is the solution for this. Any help would be much appreciated.
Thanks in advance..

Answer 1

According to the error doc error 501 is an system error inside payTm.
https://developer.paytm.com/docs/refund-status-api/
I guess you are using payTm staging server. There is nothing wrong from your side, I suggest you to wait a few hours and try again. it will automatically work

Answer 2

I was facing the same issue because i had not declared the value of PAYTM_MERCHANT_KEY
before passing it to getRefundChecksumFromArray
$checkSum = getRefundChecksumFromArray($paramList,PAYTM_MERCHANT_KEY);
This line of code solved it
define("PAYTM_MERCHANT_KEY", "your_key_goes_here");