Paypals IPN.php Error - php

Question

The situation:
Setting up a buy and download market on a website using paypal.
I've already set up the "buy" and "checkout" buttons using paypals button creator.
Now I need to create a IPN script to call paypal and verify purchase so the "product"
may start downloading. If there is a better direction in how to go about this, I would appreciate the suggestion.
The problem:
Paypals IPN sandbox simulator is giving me a
"We could not send an IPN due to an HTTP error: 500: Internal Server Error"
yet, I still receive an "INVALID" response.
The Question:
How do I
1) Fix Paypals IPN sandbox simulator to be able to send the message
2) and receive a "VERIFIED response.
The Scripts:
I am using the exact script from paypals github
heres the link:
paypal_ipn.php
Thanks in Advance!
p.s.
I have come across some similar situations but none have work for me.

Answer 1

Your IPN script must have an error in it causing it to return the 500 back to PayPal's server. Your script could be (and apparently is) handling most everything ok and saving your log file as expected, but then at the end something is causing the error so the script doesn't fully complete successfully.
The first thing I would do is solve that problem. An easy way to do this is to create your own simulator by building a basic HTML form with hidden fields that match the names of the fields you expect to get from an IPN. Set the action of the form to your IPN URL and then you can load this in a browser and submit it so that you can see the result on screen. This can help with troubleshooting and fixing any errors you have.
Once you've solved all the errors you can try the simulator again and you should get a successful result at that point. If you're still getting invalid, though, then you must have a problem with your callback to PayPal. We can figure that out once the script is completing successfully, though, and that may very well fix both problems once you figure out whatever is going on there.

Answer 2

If you are using an PHP framework to implement PayPal IPN listener, then don't forget to put exit; statement at the bottom of the controller. If you don't write exit statement, then the framework will try to load the view file, and in my case there is no view file. That is why I got the 500 Error message in the PayPal IPN simulator.
Here is example of code that is running fine on my machine.
public function ipnlistener2Action(){
// tell PHP to log errors to ipn_errors.log in this directory
//mail('YOUR EMAIL', 'Invalid IPN', "Exception");
ini_set('display_errors',1);
error_reporting(E_ALL);
// intantiate the IPN listener
require_once('common/ipnlistener.php');
$listener = new IpnListener();
// tell the IPN listener to use the PayPal test sandbox
$listener->use_sandbox = true;
// try to process the IPN POST
try {
$listener->requirePostMethod();
$verified = $listener->processIpn();
if ($verified) {
// TODO: Implement additional fraud checks and MySQL storage
mail('YOUR EMAIL', 'Valid IPN', $listener->getTextReport());
} else {
// manually investigate the invalid IPN
mail('amir.duran#ceit.co.uk', 'Invalid IPN', $listener->getTextReport());
}
} catch (Exception $e) {
mail('YOUR EMAIL', 'Invalid IPN', "Exception: ".$e->getMessage());
//var_dump("Exception");
exit(0);
}
exit;
// TODO: Handle IPN Response here
}