I have a payment acquirer in Odoo, it is working but the business wants to be able to collect a fixed processing fee for this payment acquirer (no other acquirers).

I was thinking about adding a product called Payment Fee to the sales order so that it is show in the checkout screen of the webshop, but then you have the problem if the transaction is denied and the user wishes to try another payment method, then the product should be removed again.

Have any of you done this before?