[ Gravity Forms ] When confirmation message is displayed, send Facebook Pixel custom tracking

functions.php

<?php
add_action('wp_footer', 'ching_gf_fbq' );
function ching_gf_fbq() {
// 	if show code on certain page
// 	if( ! is_page(123) )
// 		return;
?>
	<script>
		jQuery(document).ready(function(){
		  jQuery(document).on('gform_confirmation_loaded', function(event, formId) {
			  fbq('trackCustom', 'Newsletter');
		  });
		})
	</script>
<?php
}