Hi,
We didn't add yet the capability to have taxes on payment fees. It might be straight forward theoretically, but it will require to modify all the payment plugins, the display of the order data in the backend, the frontend, the emails, the invoice, and change the calculation algorithm in many other places (points system, total calculations, tax calculations, HikaMarket vendor fees, etc. So it's not a small task.
That's a feature we have on our todo list.
For the time being, you'll have to either no payment fees, or payment fees without taxes, or add these payment fees differently to the orders if possible (included the shipping methods fees for example, or as a negative auto load coupon).