How call a php API page to make it function?

I am trying to have people register at the a site and on registration a page called "mailing_list.php" sends to Email Marketer to add the user to the mailing list.

API code:

<?PHP

if ($MailingListAuth == true) {

$s_name = check_type('s_name');

$s_email = check_type('s_email');

$xml = '<xmlreques>

<username>MyAdminUserANme</username>

<usertoken>b331be66-A-TOKEN-2f1d</usertoken>

<requesttype>subscribers</requesttype>

<requestmethod>AddSubscriberToList</requestmethod>

<details>

<emailaddress>'.$s_mail.'</emailaddress>

<mailinglist>2</mailinglist>

<format>html</format>

<confirmed>yes</confirmed>

<customfields>

<item>

<fieldid>2</fieldid>

<value>'.$s_name.'</value>

</item>

</customfields>

</details>

</xmlrequest>

';

$ch = curl_init('https://example.com/mail/xml.php'); //CHANGE TO THE PATH OF YOUR IEM INSTALLATION

curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);

curl_setopt($ch, CURLOPT_POST, 1);

curl_setopt($ch, CURLOPT_POSTFIELDS, $xml);

$result = @curl_exec($ch);

if($result === false) {die("Error performing request");}

//var_dump($result); //for debugging purposes

//Example of how to display returned data

$xml_doc = simplexml_load_string($result);

if ($xml_doc->status == 'SUCCESS' && empty($xml_doc->data)) {die('Status is success. Empty response.');}

if ($xml_doc->status == 'SUCCESS') {

echo 'Response: <br />';

var_dump($xml_doc->data);

} else {

echo 'Error is '. $xml_doc->errormessage;

}

}

?>

What needs adding to registration page to get it work