[Paypal] IPN

Bonjour,

J'ai suivi le tuto Paypal. Cependant, je rencontre des problèmes avec mon IPN.

Mon IPN

<?php
$email_account = 'toto@toto.toto';

// read the post from PayPal system and add 'cmd'
$req = 'cmd=_notify-validate';

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

// post back to PayPal system to validate
$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 ('www.sandbox.paypal.com', 80, $errno, $errstr, 30);

// assign posted variables to local variables
$item_name = $_POST['item_name'];
$item_number = $_POST['item_number']; // id commande
$payment_status = $_POST['payment_status']; // Completed,
$payment_amount = $_POST['mc_gross']; //0.01
$payment_currency = $_POST['mc_currency']; //CAD
$txn_id = $_POST['txn_id'];
$receiver_email = $_POST['receiver_email'];
$payer_email = $_POST['payer_email'];
parse_str($_POST['custom'], $custom);

if (!$fp)
{
  // HTTP ERROR
  file_put_contents('log', "Erreur HTTP.");
}
else
{
  fputs ($fp, $header . $req);

    $listeRessources = '';

  while (!feof($fp))
  {
    $res = fgets ($fp, 1024);
    $listeRessources .= ' (+) '.$res;

    if (strcmp ($res, "VERIFIED") == 0) {

      if ($payment_status == "Completed")
      {

        // Check le mail crédité
        if ($email_account != $receiver_email) {
          file_put_contents('log', "Mauvais mail.");
          die();
        }

        // Check la cohérence du montant
        // .... 
        if ($payment_amount != $invoice->getPrice() ) {
          file_put_contents('log', "Mauvais prix.");
          die();
        }

        // Modification du statut de la facture
        // ....

      }

    } // End verified

    else if (strcmp ($res, "INVALID") == 0) {
      exit("Paiement invalide !");
    }

  } // End while

  fclose ($fp);
}

file_put_contents('log', "Ressources parcourues : ".$listeRessources);
?>

Problème

Cependant, en observant le log, je m'apperçois que JAMAIS le script valide la condition if (strcmp ($res, "VERIFIED") == 0) {.
Mon log, qui contient la liste des ressources traitées (sauf en cas d'erreur), contient :

Liste des ressources
(+) HTTP/1.0 302 Found
 (+) Location: https://www.sandbox.paypal.com
 (+) Server: BigIP
 (+) Connection: close
 (+) Content-Length: 0
 (+) 

Une idée du problème ? Merci !