Hallo, is it possible to set taxes on the total of the invoice and not having to set them for each item? Ideally when I create an invoice the taxes should already be set for the total.
Taxes are defined for products and services and not for invoices by law. What you want does not make any sense. If you did forget to assign taxes when creating you products, then use the mass editing module to add the taxes in bulk, use product .csv export and reimport with the proper taxes, or use the module for product category taxes and assign the proper taxes to product categories.