Quick snippet/plugin/dropin to test IPN support

ipn-test.php

<?php
/**
 * Plugin Name: PayPal Sandbox IPN Tester
 * Description: Pings the IPN endpoint to see if your server can connect. Just head to <a href="/?ipn-test=1">yoursite.com/?ipn-test=1</a> whilst logged in as admin.
 * Version: 1.0.0
 * Author: WooThemes
 * Requires at least: 4.1
 * Tested up to: 4.3
 */
if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

add_action( 'wp_loaded', 'paypal_sandbox_ipn_tester' );

function paypal_sandbox_ipn_tester() {
	if ( ! empty( $_GET['ipn-test'] ) && current_user_can( 'manage_options' ) ) {
	  $response = wp_safe_remote_post( 'https://www.sandbox.paypal.com/cgi-bin/webscr', array(
	  	'body'       => array(
	  		'test_ipn' => 1,
	  		'cmd'      => '_notify-validate'
	  	)
	  ) );

	  if ( ! is_wp_error( $response ) ) {
	  	wp_die( 'SUCCESS' );
	  } else {
	  	wp_die( 'FAIL - ' . $response->get_error_message() );
	  }
	}
}

No, they can't. Shared hosting environments need to consider more than just WordPress, as described here:
https://core.trac.wordpress.org/ticket/36320#comment:7

But here is my tentative fix anyway:

function rbst_http_api_transports() {
    return array( 'streams', 'curl' );
}
add_filter( 'http_api_transports', 'rbst_http_api_transports', 9999 );

@reidbiztech, I just copied the code in one of my plugins and tested via IPN Simulator. No luck.

Can you let me know where to past this code ? Also, I am using a relative old php version 5.4 . Could that be an issue ?

thanks for your input.

Mike

so interestingly, before adding your code to my plugin I received this error:

SSL routines:SSL23_GET_SERVER_HELLO:sslv3 alert handshake failure

after adding your code I receive this error:

FAIL - The SSL certificate for the host could not be verified.

Can you make sense of this ? Any idea where to go from here ?

thanks a lot,
Mike