Fortnox - Swish Payments as Cash Invoice

functions.php

<?php
/**
* @snippet WooCommerce - Fortnox plugin by Redlight Media - Set Terms and PaymentWay if Swish or Stripe order
* @author Redlight Media AB / Christopher Hedqvist
* @compatible WooCommerce 4.2.0
*/
function redlight_fortnox_swish_invoicetype($invoice, $order_id) {
    $order = wc_get_order($order_id);
    $order_payment_method = $order->get_payment_method();
    switch( $order_payment_method ) {
        case 'stripe':
        case 'redlight_swish':
        case 'redlight_swish-ecommerce':
            $invoice['Invoice']['InvoiceType'] = 'CASHINVOICE';
            break;
        default:
            $invoice['Invoice']['InvoiceType'] = 'INVOICE' ;
    }
    
    return $invoice;
}
add_filter('obj_fortnox_update_invoice_params', 'redlight_fortnox_swish_invoicetype', 10, 2 );