Paypal, Standard & paiement IPN

<?php
session_start();
require_once('includes/config/config.inc.php');

$req = 'cmd=_notify-validate';

foreach ($_POST as $key => $value){
  $value = urlencode(stripslashes($value));
  $req .= "&$key=$value";
}

$header .= "POST /cgi-bin/webscr HTTP/1.0\r\n";
$header .= "Content-Type: application/x-www-form-urlencoded\r\n";
$header .= "Content-Length: " . strlen($req) . "\r\n\r\n";
$fp = fsockopen ('ssl paypal website', 443, $errno, $errstr, 30);

$custom = $_POST['custom'];
$item_name = $_POST['item_name'];
$item_number = $_POST['item_number'];
$payment_status = $_POST['payment_status'];
$payment_amount = $_POST['mc_gross'];
$payment_currency = $_POST['mc_currency'];
$txn_id = $_POST['txn_id'];
$receiver_email = $_POST['receiver_email'];
$receipt_id = $_POST['receipt_id'];

if (!$fp){
   //Message
}else{
  fputs ($fp, $header . $req);
  while (!feof($fp)){
    $res = fgets ($fp, 1024);
    if (strcmp ($res, "VERIFIED") == 0){
      $Itemid = explode(",", $custom);
      $size_counter_array = sizeof($Itemid);
      foreach($Itemid as $item_new){
        $count_len = substr_count($item_new, '.');

          list($items_quantity, $item_product_id) = split('[.]', $item_new);
          )$QuerySuccess = (bool)@mysql_query("UPDATE store set quantity=(quantity - $items_quantity) WHERE id='".$item_product_id."'");
          if(QuerySuccess) echo "Success";
        }
      }
    }else if (strcmp ($res, "INVALID") == 0){
      //echo 2;
    }
  }
  fclose ($fp);
  setcookie($receipt_id,"", time()-60, "/");
}
?>