Fortnox - Set Email Address to billing email

functions.php

<?php
/**
 * @snippet       WooCommerce -Fortnox - Set customers email to Order billing emailing
 * @author        Redlight Media AB / Christopher Hedqvist
 * @compatible    WooCommerce 3.9.0
 */
function redlight_fortnox_order_email_to( $orderData, $order_id) {
    $order = wc_get_order($order_id);
    $orderData['Order']['EmailInformation']['EmailAddressTo'] = $order->get_billing_email();
    
    return $orderData;
}
add_filter('obj_fortnox_order_data', 'redlight_fortnox_order_email_to', 10, 2 );