Sometimes a message like this may appear when saving an invoice:
This message appears if you use the buttons for cost of VAT or cost of 50% VAT. This means that the VAT rate was 20% on the invoice line, but if you clicked on the cost of VAT, it will be charged with a 0% rate. If there is no difference in the gross amount on the invoice, this notification does not interfere with the further processing of the invoice.