$hash         = '';
//Below is the required format need to hash it and send it across payumoney page. UDF means User Define Fields.
//$hashSequence = "key|txnid|amount|productinfo|firstname|email|udf1|udf2|udf3|udf4|udf5|udf6|udf7|udf8|udf9|udf10";
$hash_string = MERCHANT_KEY."|".$txnid."|".$amount."|"."productinfo|".$firstName."|".$email."|||||||||||".SALT;
$hash = strtolower(hash('sha512', $hash_string));
$action = PAYU_BASE_URL . '/_payment';