Most of the eCommerce platforms allow a discount to be applied to an order.
A common scenario is a "Promo Code" being entered at check out. e.g. The Promo code will give you $50 discount on the total of your orders.
See example below:
StarShipIT will import the value of each item and the total value of the order.
However, it is not allowed to display a discount on the Customs declaration form, so the sum of the items will not reflect the discount applied. This is because you have to declare the true value of the goods for customs purposes.
See below example order now in StarShipIT
A workaround is to modify the Unit price of the items to make them match with the Total Value imported from Shopify.