Hi Nicolas, No, it doesn't work like that at all. See attached images.
The first is the sales order in Hikashop, the second is the sales receipt in Stripe.
This second one shows the facts.
As you can see the order value is incorrect. The customer either pays extra on top of the order price, OR they get a discount on the order price.
What actually needs to happen is that it is calculated in the same way as the VAT and deducted before the net figure but after the customer has paid the full price for the item. Then the amount left for the Vendor fee to be calculated is going to be 2.60 euros (net of the VAT and CC Fee).
I can't see any other way to do it. It MUST be treated in the same way as the VAT whichever way you work it.