PayPal IPN php always INVALID - php

Question

I've made an attempt at writing a small PayPal IPN handler however I'm always getting 'INVALID' when using the IPN simulator https://developer.paypal.com/webapps/developer/applications/ipn_simulator . I'm not sure what about the URL I'm sending back isn't right. I have looked at some Gists for this topic but they all seem a little long winded. Their docs on this are here https://developer.paypal.com/webapps/developer/docs/classic/ipn/integration-guide/IPNIntro/#protocol_and_arch and I think that I have followed all the steps for the protocol.
Any help is appreciated
<?php
/**
* Validates a PayPal IPN notification
* #param array $req The $_POST variable for the request
* #return String Returns the validity: 'VALID' or 'INVALID'
*/
function verifyPayPalIPN($req) {
// Base URL for the php validation
$baseURL = 'https://www.paypal.com/cgi-bin/webscr?cmd=_notify-validate';
// Loop through the POST parameters to
// create the validaton URL
$postVars = '';
foreach ($req as $key => $value) {
$postVars .= $key . '=' . urlencode($value) . '&';
}
// Strip the last & off of the URL
$postVars = substr($postVars, 0, -1);
// Send the request to PayPal to confirm
// whether the request to the script is
// from PayPal
$requestValidity = system("curl --data '$postVars' $baseURL");
return $requestValidity;
}
file_put_contents('/tmp/result.txt', verifyPayPalIPN($_POST));
?>

Answer 1

cmd=_notify-validate should be part of your postVars string
$baseURL = 'https://www.paypal.com/cgi-bin/webscr';
// Loop through the POST parameters to
// create the validaton URL
$postVars = 'cmd=_notify-validate';
foreach ($req as $key => $value) {
$postVars .= $key . '=' . urlencode($value) . '&';
}
The code that I have used in the past is this:
$req = 'cmd=_notify-validate';
foreach ($_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.paypal.com", 443, $errno, $errstr, 30);
if (!$fp) {
// HTTP ERROR
} else {
fputs ($fp, $header . $req);
while (!feof($fp)) {
$res = fgets ($fp, 1024);
if (strcmp ($res, "VERIFIED") == 0) {
} else if (strcmp ($res, "INVALID") == 0) {
}
}
fclose($fp);
}
Note the port no. 443 also

Answer 2

firstly, check if your paying enviroment and validating enviroment is the same (both sandbox or both production), if they are not, say your customer paid their order in an production enviroment, but then your PHP code trying to request a sandbox enviroment end point to verify the IPN request, then it will always end as INVALIDE