Paypal IPN get empty POST data - paypal

Question

I am using the sandbox environment and the code for my IPN listener is from https://github.com/paypal/ipn-code-samples/blob/master/paypal_ipn.php
After the sandbox transaction complete, I get empty $_POST while receive $_GET instead.
Array
(
[tx] => 14M290096L261713C
[st] => Pending
[amt] => 1.00
[cc] => USD
[cm] =>
[item_number] =>
)
It's confusing me because it's not safe passing data using GET method. I've changed the button encoding language to utf-8 and my listener passed the IPN simulator.
After searching any possible solution online I found this blog article, and in the tutorial it received $_GET data as well. It makes me wonder if it's also a suggested way to do IPN listening using GET.
Here's my Paypal button code:
<form action="https://www.sandbox.paypal.com/cgi-bin/webscr" method="post" target="_top">
<input type="hidden" name="charset" value="utf-8">
<input type="hidden" name="cmd" value="_s-xclick">
<input type="hidden" name="hosted_button_id" value="A5HMGXMJNWR7Y">
<table>
<tr><td><input type="hidden" name="on0" value="Plan">Plan</td></tr><tr><td><select name="os0">
<option value="Basic">Basic $1.00 USD</option>
<option value="Advacned">Advacned $2.00 USD</option>
<option value="Premium">Premium $3.00 USD</option>
</select> </td></tr>
</table>
<input type="hidden" name="currency_code" value="USD">
<input type="image" src="https://www.sandbox.paypal.com/en_US/i/btn/btn_buynowCC_LG.gif" border="0" name="submit" alt="PayPal - The safer, easier way to pay online!">
<img alt="" border="0" src="https://www.sandbox.paypal.com/en_US/i/scr/pixel.gif" width="1" height="1">
</form>
Did I miss something? Thanks for the help.

Answer 1

It's been a while for me, but IPN is not PDT, the blog article is PDT.
Which/when to use PDT and/or IPN
See IPN info/detail here.
The key items to understand about IPN are:
IPN is an asynchronous message service, meaning that IPNs are not synchronized with actions on your website....
The IPN message service is not a real-time service. As a result, your listener may not receive an IPN message for many seconds after an event occurs. As a result, your checkout flow should not depend upon receiving an IPN message to complete. If it does, your checkout flow will be slow during periods of heavy system load and complicated, since it must handle retries.
hth..