Paypal sandbox not giving a responce - paypal

Question

I know this has been covered quite a lot on here but I've spent most of the day trying to fix this error and don't seem to be getting anywhere.
When I use the PayPals IPN simulator to send a Simulation IPN I keep receiving the response Live-INVALID IPN
Now I thought that this was due to the fact that I'm sending it as a test from sandbox so I tried using the sandbox url as you can see below but if I do this I don't receive a responce at all.
Can someone tell me where I'm going wrong please?
<?php // PHP 4.1
// 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";
}
$email = ****;
// 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.paypal.com', 443, $errno, $errstr, 30);
//$fp = fsockopen ('ssl://www.sandbox.paypal.com', 443, $errno, $errstr, 30);
// assign posted variables to local 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) {
// HTTP ERROR
} else {
fputs ($fp, $header . $req);
while (!feof($fp)) {
$res = fgets ($fp, 1024);
if (strcmp ($res, "VERIFIED") == 0) {
// check the payment_status is Completed
// check that txn_id has not been previously processed
// check that receiver_email is your Primary PayPal email
// check that payment_amount/payment_currency are correct
// process payment
mail($email, "Live-VERIFIED IPN", $res . "\n\n" . $req);
}
else if (strcmp ($res, "INVALID") == 0) {
// log for manual investigation
mail($email, "Live-INVALID IPN", $res . "\n\n" . $req);
}
}
fclose ($fp);
}
?>

Answer 1

After posting this question I found the following example on paypal developers which uses curl instead, this worked first time for me and I received a response of verified.
Please find the link below for anyone who encounters the same issue:
https://developer.paypal.com/webapps/developer/docs/classic/ipn/ht_ipn/