Hi madein83,
Apologies in advance for the long response 
The way an IPN works is broken into 2 steps:
first an IPN message will be received by your script, the script then sends this same IPN back to PayPal to see if it actually came from PayPal or not;
PayPal will respond with either “VERIFIED” or “INVALID”;
So looking at your script:
when the IPN listener receives the first message, it assigns it into $req;
then it sends this message back to PayPal and receives another message (either “VERIFIED” or “INVALID”) and places that into the variable $res.
So far so good!
After this point any processing should be done using the first variable that you assigned the POST variables to $req; (the $res variable may not contain the values that you want)
One thing to take note of is that you must be sure that you are sending the original IPN POST message to the correct end point, i.e. if you are swopping between working in sandbox/Live, you will have to change 2 parts of your script the $header and the $fp endpoint.
Here is a full working script for sandbox that will email you back the IPN message and whether it is verified or not, the only thing that you need to change are both of the $mail_To variables (to your own email address)
<?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";
// If testing on Sandbox use:
$header .= "Host: www.sandbox.paypal.com:443\r\n";
// $header .= "Host: www.paypal.com:443\r\n";
$header .= "Content-Type: application/x-www-form-urlencoded\r\n";
$header .= "Content-Length: " . strlen($req) . "\r\n\r\n";
// If testing on Sandbox use:
$fp = fsockopen ('ssl://www.sandbox.paypal.com', 443, $errno, $errstr, 30);
// $fp = fsockopen ('ssl://www.paypal.com', 443, $errno, $errstr, 30);
if (!$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_From = "From: sandbox@pptest.com";
$mail_To = "YourEmailAddress@YourDomain.com";
$mail_Subject = "VERIFIED IPN";
$mail_Body = $req;
foreach ($_POST as $key => $value){
$emailtext .= $key . " = " .$value ."\n\n";
}
mail($mail_To, $mail_Subject, $emailtext . "\n\n" . $mail_Body, $mail_From);
}
else if (strcmp ($res, "INVALID") == 0) {
// log for manual investigation
$mail_From = "From: sandbox@pptest.com";
$mail_To = "YourEmailAddress@YourDomain.com";
$mail_Subject = "INVALID IPN";
$mail_Body = $req;
foreach ($_POST as $key => $value){
$emailtext .= $key . " = " .$value ."\n\n";
}
mail($mail_To, $mail_Subject, $emailtext . "\n\n" . $mail_Body, $mail_From);
}
}
fclose ($fp);
}
?>
Try out the above script for testing, making note of two things:
Remember to change the 2 places in the script if you are moving from sandbox to live;
Don’t forget to have a look in your junk mail folder as IPN messages received often end up there!
Please let me know if this helps
Paula
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