Paypal IPN: INVALID

Hi experts, I'm trying to use the IPN Paypal system.
I've tryed different code... but always the same answer: INVALID.

The strange thing is that the PayPal manual say that Paypal pass the parameters in POST... but I get anything in POST, I get data only in GET.

Here is my code:

<?php

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

foreach ($_GET 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 .= "Host: www.sandbox.paypal.com\r\n"; //<<<<<<<<<<<< ADD THIS LINE
$header .= "Referer: ".$_SERVER['HTTP_HOST'].$_SERVER['PHP_SELF'].@$_SERVER['QUERY_STRING']."\r\n";
$header .= "Server: ".$_SERVER['SERVER_SOFTWARE']."\r\n";
$header .= "Content-Type: application/x-www-form-urlencoded\r\n";
$header .= "Content-Length: " . strlen($req) . "\r\n";
$header .= "Accept: */*\r\n\r\n";

$fp = fsockopen ('www.sandbox.paypal.com', 80, $errno, $errstr, 30);

if (!$fp) {
      echo "PHP fsockopen() error: " . $errstr;
}
else {
      fputs ($fp, $header . $req);
      while (!feof($fp)) {
            $res = fgets ($fp, 1024);
            echo "RECEIVED: ".$res."<BR>"; // for debug
            if (strcmp ($res, "VERIFIED") == 0) {
                  echo "VERIFIED";
            }
            else if (strcmp ($res, "INVALID") == 0) {
                  echo "INVALID";
            }
      }
}

?>


Here the answer:

cmd=_notify-validate&tx=9BL62873GK243402G&st=Completed&amt=100.00&cc=EUR&cm=&sig=rD%2fvVjLNDwD3dAm9sv9GPPiTyAvtYm4fcqJBqXhwWoV0Y1nyEkWDRsuJg2102NpBwPjDp0sARhPOF446Z6hfW8xzv3S%2f1ILdF1v964dm0M%2fCXItrhJI2RsD7d63EgMeVPRn8TZ4ndlrmEtCBvtLT8QOlViCPOoPCwgGhXd9I%2bM8%3dRECEIVED: HTTP/1.0 200 OK
RECEIVED: Date: Mon, 19 Jun 2006 16:53:49 GMT
RECEIVED: Server: Apache/1.3.27 (Unix) mod_ssl/2.8.12 OpenSSL/0.9.7a PHP/4.3.2
RECEIVED: Set-Cookie: cookie_check=yes; expires=Thu, 16-Jun-2016 16:53:49 GMT; path=/; domain=.paypal.com
RECEIVED: Set-Cookie: Apache=64.202.165.201.153601150736029465; path=/; expires=Wed, 11-Jun-36 16:53:49 GMT
RECEIVED: Content-Type: text/html; charset=UTF-8
RECEIVED: X-Cache: MISS from wc04.inet.mesa1.secureserver.net
RECEIVED: Connection: close
RECEIVED:
RECEIVED: INVALID


Thanks