Paypal PDT -没有收到响应(PHP)

用户付款后返回到此页面:

// read the post from PayPal system and add 'cmd'
$req = 'cmd=_notify-synch';
$tx_token = $_GET['tx'];
$auth_token = "REMOVEDFROMQUESTION";
$req .= "&tx=$tx_token&at=$auth_token";
// 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";
// url for paypal sandbox
$fp = fsockopen ('www.sandbox.paypal.com', 80, $errno, $errstr, 30);    
// url for payal
// $fp = fsockopen ('www.paypal.com', 80, $errno, $errstr, 30);
// If possible, securely post back to paypal using HTTPS
// Your PHP server will need to be SSL enabled
// $fp = fsockopen ('ssl://www.paypal.com', 443, $errno, $errstr, 30);
if (!$fp) {
    // HTTP ERROR
    echo "http error";
} else {
    fputs ($fp, $header . $req);
    // read the body data
    $res = '';
    $headerdone = false;
    while (!feof($fp)) {
        $line = fgets ($fp, 1024);
        if (strcmp($line, "'r'n") == 0) {
            // read the header
            $headerdone = true;
        }
        else if ($headerdone) {
            // header has been read. now read the contents
            $res .= $line;
        }
    }
    // parse the data
    $lines = explode("'n", $res);
    $keyarray = array();
    if (strcmp ($lines[0], "SUCCESS") == 0) {
        for ($i=1; $i<count($lines);$i++){
            list($key,$val) = explode("=", $lines[$i]);
            $keyarray[urldecode($key)] = urldecode($val);
        }
        // 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
        $firstname = $keyarray['first_name'];
        $lastname = $keyarray['last_name'];
        $itemname = $keyarray['item_name'];
        $amount = $keyarray['payment_gross'];
        echo ("<p><h3>Thank you for your purchase!</h3></p>");
        echo ("<b>Payment Details</b><br>'n");
        echo ("<li>Name: $firstname $lastname</li>'n");
        echo ("<li>Item: $itemname</li>'n");
        echo ("<li>Amount: $amount</li>'n");
        echo ("");
    }
    else if (strcmp ($lines[0], "FAIL") == 0) {
        // log for manual investigation
        echo "fail";
    } else {
        echo "fail2";
    }
}
fclose ($fp);

Paypal使用正确的GET变量成功将用户返回到页面:

?status=success&tx=203229VT863344T&st=Pending&amt=76.00&cc=GBP&cm=19&item_number=

但是当脚本运行时，它返回"error2"。当我尝试输出响应时，我一无所获。

谢谢你的帮助