PayPal IPN不是“；验证”；或“；无效”；

我正在尝试在网站上集成PayPal IPN。出于某种原因，IPN侦听器既没有验证付款，也没有将其标记为无效。我在代码中的不同位置放置了mail()函数，以通知我有多少程序正在运行。

我已经尝试过在$res变量上使用和不使用trim()。两种方式都失败了。

这是我的代码：

    $req = 'cmd=_notify-validate';
    foreach ($_POST as $key => $value) {
        $value = urlencode(stripslashes($value));
        $req .= "&$key=$value";
    }
    mail('test@test.net', 0, 0); //EMAIL RECEIVED
    $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://www.sandbox.paypal.com', 443, $errno, $errstr, 30);
    $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'];
    $payer_email = $_POST['payer_email'];
    $first_name = $_POST['first_name'];
    $last_name = $_POST['last_name'];
    $address_street = $_POST['address_street'];
    $address_city = $_POST['address_city'];
    $address_zip = $_POST['address_zip'];
    $address_state = $_POST['address_state'];
    $address_country = $_POST['address_country'];
    $contact_phone = $_POST['contact_phone'];
    $payer_id = $_POST['payer_id'];

    if (!$fp) {
        //HTTP Error
        mail('test@test.net', 1, 1);
    } else {
        fputs ($fp, $header . $req);
        mail('test@test.net', 2, 2); //EMAIL RECEIVED
        while (!feof($fp)) {
            $res = fgets ($fp, 1024);
            if (strcmp (trim($res), "VERIFIED") == 0) {
                mail('test@test.net', 3, 3);
            } else if (strcmp (trim($res), "INVALID") == 0) {
                mail('test@test.net', 4, 4);
            } else {
                mail('test@test.net', 5, 5); //EMAIL RECEIVED
            }
        }
        fclose ($fp);
    }
}

我收到的电子邮件分别是0、2和5。