PrestaShop/PrestaShop-modules — pull request #120 by riccardo91 (2013-11-07 13:58:27+00:00)
Title: Update notifier.php

Reading POSTed data directly from $_POST causes serialization issues with array data in the POST.
Instead, read raw POST data from the input stream.

official documentation paypal
https://developer.paypal.com/docs/classic/ipn/ht_ipn/