WPAI-func.php

<?php 
function set_parent_id($id){

 
 	$parent_id = get_field('parent_id', $id);

 	$args = array(
		'posts_per_page' =>1,
		'post_type' => 'page',
		'meta_query' => array(
			array(
			'key' => 'entry_id',
			'value' => $parent_id,
			'compare' => '='
			),
		)
	);

	query_posts($args); 

	while (have_posts()) : the_post(); 
		$wp_parent_id = get_the_id();
		update_post_meta($id, 'wp_parent_id', $wp_parent_id);
	endwhile;


 }

add_action('pxmi_saved_post', 'set_parent_id', 10, 1);
add_action('pmxi_update_post_meta', 'set_parent_id', 10, 1);
?>