Paypal IPN Sandbox无法正常工作

Question

I've been searching the forums but have had no luck using Sandbox IPN to get a response. I've followed many tips but can't get things working - it looks like the www.sandbox.paypal.com isn't working/responding as if I use production I get an IPN Invalid response as expected. You can see the commented out lines of code in my example below.

Does anyone have any idea why this may not be working?

<?php 
error_reporting(E_ALL ^ E_NOTICE);
ini_set('display_errors', '1'); 
$email = "[e-mail]"; 
$header = ""; 
$emailtext = ""; 
// Read the post from PayPal and add 'cmd' 
$req = 'cmd=_notify-validate'; 

if(function_exists('get_magic_quotes_gpc')) 
{ 
    $get_magic_quotes_exits = true;
} 

foreach ($_POST as $key => $value) // Handle escape characters, which depends on setting of magic quotes 
{ 
    if($get_magic_quotes_exists == true && get_magic_quotes_gpc() == 1) 
    { 
        $value = urlencode(stripslashes($value)); 
    } else { 
        $value = urlencode($value); 
    } 
    $req .= "&$key=$value"; 
} 

// Post back to PayPal to validate 
/*
$header .= "POST /cgi-bin/webscr HTTP/1.0
"; 
$header .= "Content-Type: application/x-www-form-urlencoded
"; 
$header .= "Content-Length: " . strlen($req) . "

"; 
*/

$header = "POST /cgi-bin/webscr HTTP/1.1
";
$header .= "Content-Type: application/x-www-form-urlencoded
";
$header .= "Host: www.sandbox.paypal.com
";  // www.paypal.com for a live site
$header .= "Content-Length: " . strlen($req) . "
";
$header .= "Connection: close

";

//$fp = fsockopen ('www.paypal.com', 80, $errno, $errstr, 30); 
$fp = fsockopen ('ssl://www.sandbox.paypal.com', 443, $errno, $errstr, 30)

// Process validation from PayPal 
if (!$fp) { 
// HTTP ERROR 
} else { 
// NO HTTP ERROR 
    fputs ($fp, $header . $req); 

    while (!feof($fp)) { 
         $res = fgets ($fp, 1024); 
         if (stripos($res, "VERIFIED") !== false){
         //if (strcmp ($res, "VERIFIED") == 0) { 
             // TODO: 
             // Check the payment_status is Completed 
             // Check that txn_id has not been previously processed 
             // Check that receiver_email is your Primary PayPal email 
             // Check that payment_amount/payment_currency are correct 
             // Process payment 
            // If 'VERIFIED', send an email of IPN variables and values to the 
            // specified email address 
            foreach ($_POST as $key => $value){ 
            $emailtext .= $key . " = " .$value ."

"; 
            } 
            mail($email, "Live-VERIFIED IPN", $emailtext . "

" . $req); 
        //} else if (strcmp ($res, "INVALID") == 0) { 
        } else if (stripos($res, "VERIFIED") !== false){
        // If 'INVALID', send an email. TODO: Log for manual investigation. 
            foreach ($_POST as $key => $value){ 
                $emailtext .= $key . " = " .$value ."

";
            } 
            mail($email, "Live-INVALID IPN", $emailtext . "

" . $req); 
        } 

    } 
    fclose ($fp);
}

?>