This field can only be entered when the following conditions are met:
You use this field to indicate if the customer is subject to article 23 of the Portuguese law 71/2013 on VAT rules. If yes, all invoices sent to this customer will go through a specific process at the payment level, once the invoices have been settled. The payments must indeed be subject to a tax return, which means that the customer must be provided with a special payment notice listing all VAT amounts by tax level.