Custom field to REGISTRED USERS in Fortnox

functions.php

<?php
/**
  * @snippet       WooCommerce - Fortnox plugin by Redlight Media - (REGISTRED USERS) Set $our_custom_field as Comment field to Fortnox via functions.php
  * @author        Redlight Media AB / Christopher Hedqvist
  * @compatible    WooCommerce 3.0.6
  */
function redlight_custom_customerdata( $customer) {

     $our_custom_field = (!empty($_POST['our_custom_field'])) ? $_POST['our_custom_field'] : "";

    if(isset($our_custom_field)){
        $customer['Customer']['Comments'] = $our_custom_field;
    }

     return $customer;
}
add_filter( 'obj_fortnox_customer_data', 'redlight_custom_customerdata');