The VAT Margin Scheme tax that is usually applied in the EU territory is the difference between what you paid for an item and what you sold it for, rather than the full selling price.
RepairDesk iPad POS allows activating VAT Margin for specific
categories and for specific products from the web interface. To know how this feature works on web app, please refer to knowledge base article.
When VAT Margin is applied to any product or category, the profit against that product/category is shown in cart as shown below.
Please note that VAT tax class has the priority over all other tax classes applied to the product and categories. If you have enabled VAT against a product or category from web, then you will not be able to change its tax class from iPad.