bidirectional with user and post -pods

UserToPost.php

add_action( 'pods_api_post_save_pod_item', 'slug_user_fix', 10, 3); // Needed to add the params number
function slug_user_fix( $pieces, $is_new_item, $id ) {
	if ( isset( $pieces[ 'fields' ][ 'FIELD_REALTED_TO_USERS' ][ 'value' ] ) ) {
    $uIDs = explode(",", $pieces[ 'fields' ][ 'FIELD_RELATED_TO_USERS' ][ 'value' ]);

    // Check that we have some uIDs to work with.
    if (false === empty($uIDs)) {
        // Loop through, converting to integers and verifying the conversion
        foreach($uIDs as $uID) {
            $uID = (int)$uID;
            if (is_int($uID)) {
                if (get_user_by('id', $uID) !== false) {
                    $value = get_user_meta($uID, 'RELATED_FIELD_IN_USERS_NAME.ID');
                    $value[] = $id;
                    update_user_meta($uID, 'RELATED_FIELD_IN_USERS_NAME', $value);
                }

            }
        }
    }
}

return $pieces;
}