Help with configuring NGINX for use with Paypal IPN Forwarder - Prosites 3.5.1.6 multiple networks

Hey guys,

So I have been trying to get the Paypal IPN forwarder (2014 version) to work on my NGINX setup for an embarrassing couple of months. I have read all the threads over and over. Here is where its at: When I run a sandbox transaction the "POST" returns HTTP response code 302 "temporary redirect" at the server access log and forwarder log, Paypal's response code is 503. The IPN is all functional when direct to the listener. I think I need a return directive on my NGINX config to solve this or am missing something.

Incidentally the site does upgrade to pro, registers all 4 actions in the manage site log, and all emails are triggered, Paypal posts the transaction and recurring profile, however the PP notifier continues to retry 8 times and triggers 8 pdf email receipts as its was returned HTTP 503.

Server access log:
xx.xxx.xxx.151 - - [28/Nov/2015:11:12:51 +0700] "POST /wp-admin/admin-ajax.php?action=psts_pypl_ipn HTTP/1.1" 302 5 "-" "-"
xx.xxx.xxx.151 - - [28/Nov/2015:11:13:19 +0700] "POST /wp-admin/admin-ajax.php?action=psts_pypl_ipn HTTP/1.1" 302 5 "-" "-"

Script log:
[2015-11-28 04:38:05] Could not contact mysite1.com/wp-admin/admin-ajax.php?action=psts_pypl_ipn to send the IPN: HTTP/1.1 302 Moved Temporarily

SYSTEM INFO:
PHP 5.5.30
MYSQL 5.5.46
WORDPRESS 4.3.1
NGINX 1.8.0
PROSITES 3.5.1.6

FORWARDER SCRIPT: ipn/ipn-forwarder.php

//Our password. Check for this in your script to make sure it's from us ($_POST['inc_pass']). Do not change!
define('INC_PASS', 'randompassword');

// An array of prefix to search for, domain and path to post to, and whether we're using sandbox or not for applications
$apps = array(
/* App 1 */
array('prefix' => 'mysite1',
'domain' => 'mysite1.com',
'path' => '/wp-admin/admin-ajax.php?action=psts_pypl_ipn',
'live' => false),

/* App2 */
array('prefix' => 'app2',
'domain' => 'myothersite.com',
'path' => '/ipn-handler.php',
'live' => false)
);

wp-config:
/* Paypal Ipn Forwarder */
define('PSTS_IPN_PASSWORD', 'randompassword');
define('PSTS_PYPL_PREFIX', 'mysite1');

Troubleshooting:
>Drop Plugins/Theme 2015
>Run the script on offsite server - LAMP.
>Folder permissions
>Wipe server cache
>Place the forwarder in the root directory

>Protocol variables:
array('prefix' => 'myprefix',
'domain' => 'mysite1.com',
'path' => '/wp-admin/admin-ajax.php?action=psts_pypl_ipn',
'live' => false),

array('prefix' => 'myprefix',
'domain' => 'https://mysite1.com',
'path' => '/wp-admin/admin-ajax.php?action=psts_pypl_ipn',
'live' => false),

Paypal's IPN URL:
https://mysite1.com/ipn/ipn-forwarder.php
mysite1.com/ipn/ipn-forwarder.php

I have attached the NGINX config for review. Super grateful for the script and would love to get it working and i'm stumped, help would be great - thanks.