Salve a tutti...
Mi spiegate il motivo in cui non funziona ma correggendo cambiando un codice funziona ma vorrei capire la differenza ed è utile..

Allora, ho creato un sito e-commerce tramite paypal, siccome sto facendo prove con SANDBOX PAYPAL che 5 anni fa, funzionava benissimo e adesso, all'improvviso non funge, di seguito sotto trovi il codice PHP IPN

<?php

$req = 'cmd=_notify-validate';

foreach($_POST as $key => $value)
{

$value = urlencode(stripslashes($value));
$req .= "&". $key ."=". $value ."";

}

$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.paypal.com", 443, $errno, $errstr, 30);



// assign posted variables to local variables
$item_name = $_POST['item_name'];
$business = $_POST['business'];
$item_number = $_POST['item_number'];
$payment_status = $_POST['payment_status'];
$mc_gross = $_POST['mc_gross'];
$mc_shipping = $_POST['mc_shipping'];
$payment_currency = $_POST['mc_currency'];
$txn_id = $_POST['txn_id'];
$receiver_email = $_POST['receiver_email'];
$receiver_id = $_POST['receiver_id'];
$quantity = $_POST['quantity'];
$num_cart_items = $_POST['num_cart_items'];
$payment_date = $_POST['payment_date'];
$first_name = $_POST['first_name'];
$last_name = $_POST['last_name'];
$payment_type = $_POST['payment_type'];
$payment_status = $_POST['payment_status'];
$payment_gross = $_POST['payment_gross'];
$payment_fee = $_POST['payment_fee'];
$settle_amount = $_POST['settle_amount'];
$memo = $_POST['memo'];
$shipping = $_POST['shipping'];
$payer_email = $_POST['payer_email'];
$txn_type = $_POST['txn_type'];
$payer_status = $_POST['payer_status'];
$address_street = $_POST['address_street'];
$address_city = $_POST['address_city'];
$address_state = $_POST['address_state'];
$address_zip = $_POST['address_zip'];
$address_country = $_POST['address_country'];
$address_status = $_POST['address_status'];
$item_number = $_POST['item_number'];
$tax = $_POST['tax'];
$option_name1 = $_POST['option_name1'];
$option_selection1 = $_POST['option_selection1'];
$option_name2 = $_POST['option_name2'];
$option_selection2 = $_POST['option_selection2'];
$for_auction = $_POST['for_auction'];
$invoice = $_POST['invoice'];
$custom = $_POST['custom'];
$notify_version = $_POST['notify_version'];
$verify_sign = $_POST['verify_sign'];
$payer_business_name = $_POST['payer_business_name'];
$payer_id =$_POST['payer_id'];
$mc_currency = $_POST['mc_currency'];
$mc_fee = $_POST['mc_fee'];
$exchange_rate = $_POST['exchange_rate'];
$settle_currency = $_POST['settle_currency'];
$parent_txn_id = $_POST['parent_txn_id'];
$pending_reason = $_POST['pending_reason'];
$reason_code = $_POST['reason_code'];
$night_phone_a = $_POST['night_phone_a'];
$night_phone_b= $_POST['night_phone_b'];
$day_phone_a = $_POST['day_phone_a'];
$day_phone_b = $_POST['day_phone_b'];
$contact_phone = $_POST['contact_phone'];


// subscription specific vars

$subscr_id = $_POST['subscr_id'];
$subscr_date = $_POST['subscr_date'];
$subscr_effective = $_POST['subscr_effective'];
$period1 = $_POST['period1'];
$period2 = $_POST['period2'];
$period3 = $_POST['period3'];
$amount1 = $_POST['amount1'];
$amount2 = $_POST['amount2'];
$amount3 = $_POST['amount3'];
$shipping1 = $_POST['shipping1'];
$shipping2 = $_POST['shipping2'];
$shipping3 = $_POST['shipping3'];
$mc_amount1 = $_POST['mc_amount1'];
$mc_amount2 = $_POST['mc_amount2'];
$mc_amount3 = $_POST['mc_amount3'];
$recurring = $_POST['recurring'];
$reattempt = $_POST['reattempt'];
$retry_at = $_POST['retry_at'];
$recur_times = $_POST['recur_times'];
$username = $_POST['username'];
$password = $_POST['password'];

//auction specific vars

$for_auction = $_POST['for_auction'];
$auction_closing_date = $_POST['auction_closing_date'];
$auction_multi_item = $_POST['auction_multi_item'];
$auction_buyer_id = $_POST['auction_buyer_id'];




if(!$fp)
{


} else {

fputs ($fp, $header . $req);

while(!feof($fp))
{

$res = fgets ($fp, 1024);

if(strpos($res, "VERIFIED") == 0)
{


$to = "aa@aa.it";

$subject = "prova";

$message = $collegamento_paypal ." - ". $item_number ." - ". $mc_gross;

$headers = "MIME-Version: 1.0\n";
$headers .= "Content-type: text/html; charset=iso-8859-1\n";
$headers .= "From: aa@aa.itm\n";

mail($to, $subject, $message, $headers);




} elseif(strcmp ($res, "INVALID") == 0)
{



}

}

fclose ($fp);

}

?>

Il codice STRCMP
if(strcmp($res, "VERIFIED") == 0)
Non funziona mentre se cambio da STRCMP in STRPOS

Funziona, perchè?
Mi puoi aiutare?