Add EAN code to article in Fortnox

functions.php

<?php
 /**
 * @snippet       WooCommerce - Fortnox plugin by Redlight Media - Add EAN code to article in Fortnox via functions.php
 * @author        Redlight Media AB / Christopher Hedqvist
 * @compatible    WooCommerce 3.2.6
 */
function redlight_fortnox_ean( $article, $product_id) {

    $ean_string = get_post_meta( $product_id, 'EAN', true );
    $article['Article']['EAN'] = $ean_string;

    return $article;
}
add_filter('obj_fortnox_article_data', 'redlight_fortnox_ean', 10, 2 );