gform after submission not working

I have a form that needs to be posted to third party. The code appears to be ignored. Here is the code I added to bottom of functions.php

add_action('gform_after_submission_4', 'post_to_third_party', 10, 2);
function post_to_third_party($entry, $form) {

    $post_url = 'third party url here. real url removed for security';
    $body = array(
        'CustomFields[40]' => $entry['input_1'], // first name
        'CustomFields[41]' => $entry['input_2'], // last name
        'CustomFields[44]' => $entry['input_3'], // organization name
        'CustomFields[42]' => $entry['input_4'], // phone
        'email' => $entry['input_5']  // email
        );

    $request = new WP_Http();
    $response = $request->post($post_url, array('body' => $body));

The form has been setup on this page http://dev10.swd.ca/resources/articles/

Please advise. Thank you.

You mean simply changing
gform_after_submission to gform_post_submission

and leave everything else as is? I tried this and it does not work.