Empty Result Curl in php - php

Question

I'm having a problem with PHP's cURL returning an empty string with some URL's
i want to coonect this api and i give the empty result, anyone can help me ?
<?php
$clTrid="TEST-23233434343";
$nictoken="6661361102210630";
$contact="Test-irnic";
$xml = '<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
<command>
<check>
<contact:info xmlns:contact="http://epp.nic.ir/ns/contact-1.0">
<contact:id>' . $contact . '</contact:id>
<contact:pw>' . $nictoken . '</contact:pw>
</contact:authInfo>
</contact:check>
</check>
<clTRID>' . $clTrid . '</clTRID>
</command>
</epp>';
$url = 'https://epp.nic.ir/submit';
$curl = curl_init($url);
curl_setopt ($curl, CURLOPT_HTTPHEADER, array("Content-Type: text/xml"));
curl_setopt($curl, CURLOPT_POST, true);
curl_setopt($curl, CURLOPT_POSTFIELDS, $xml);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
$result = curl_exec($curl);
if (curl_errno($curl)) {
$error_msg = curl_error($curl);
}
else echo " No Error ! ";
if(curl_errno($curl)){
throw new Exception(curl_error($curl));
}
curl_close($curl);
echo $result;
var_dump($result);
?>