PHP - 貝寶IPN總是返回無效

這是我第一次處理貝寶IPN。我瀏覽過網頁獲得了一些幫助，並且遇到了以下代碼。我花了一段時間，它總是返回無效。我想知道，但這也可能與我在Paypal上選擇的設置有關嗎？我所有啓用的是IPN和重定向。PHP - 貝寶IPN總是返回無效

<?php 
    // 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('ssl://www.sandbox.paypal.com', 443, $errno, $errstr, 30); 


    //handle variables 
    $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']; 

    if (!$fp) { 
     echo $errstr.' ('.$errno.').<br />'; 
    } else { 
     fputs ($fp, $header . $req); 
     while (!feof($fp)) { 
     $res = fgets($fp, 1024); 
     if (strcmp ($res, "VERIFIED") == 0) { 
      echo "Verified"; 
      if(strcmp($payment_status, 'Completed') == 0) { 
       if(strcmp($payment_currency, 'USD') == 0) { 
         //process data 
       } 
      } 
     } elseif(strcmp ($res, "INVALID") == 0) { 
      echo "Invalid"; 
     } 
     } 
     fclose ($fp); 
    } 
    ?>

來源

2016-02-22 George