Fortnox - Invoice Specials

functions.php

<?php
/**
* @snippet WooCommerce - Fortnox plugin by Redlight Media - Set Terms and PaymentWay if Swish order
* @author Redlight Media AB / Christopher Hedqvist
* @compatible WooCommerce 3.9.2
*/
function redlight_fortnox_payment_method_invoicetype($invoice, $order_id) {
    $order = new WC_Order($order_id);
    $order_payment_method = $order->get_payment_method();
    switch( $order_payment_method ) {
        case 'redlight_swish':
        case 'redlight_swish-ecommerce':
            $invoice['Invoice']['InvoiceType'] = 'CASHINVOICE';
            $invoice['Invoice']['TermsOfPayment'] = '0';
            $invoice['Invoice']['PaymentWay'] = 'SW';
            break;
        default:
            $invoice['Invoice']['InvoiceType'] = 'INVOICE' ;
    }
    
    return $invoice;
}
add_filter('obj_fortnox_update_invoice_params', 'redlight_fortnox_payment_method_invoicetype', 10, 2 );