If you create a full or a partial refund and don't select a specific item, that you want to refund, Shopify doesn’t attribute any tax data to this refund, which creates discrepancies in invoice management and accounting later on.

Select the product and quantity that you are refunding, instead of just typing in the exact amount to be paid to the customer.

The idea is to always select specific items, so the tax data will be displayed in the Shopify order details too. When the tax data are in Shopify, they will get correctly into Fakturoid.