This is good! Just tested some payments with and without fees application and now it seems working correctly.
It would be really good if the fees were accounted as an addition to order amount (it is deducted actually). In terms of accounting it is more clean (and it avoids to add a price to a product because of a fee) for the admin and transparent for clients. No problem if it is not indicated in a first time in checkout page as a separate indicatiom, but at least in accounting, in transactions list from admin side and client side.
In any case, thank you very much for your support, trully appreciated.