How to change a additional fee to a discount in a Payment method(solved)

Hi!

If I want to place a discount in PayInStore payment method or to define a negative value to additional fee?
I want to offer a discount in order "subtotal" for the customer which make a deposit directly in my bank account (sure this only is possible for older customer which have enough trust with the store).
Then I think: I go to place a negative value in PayInStore method and rename it to Account Deposit and to give the necessary info to the customer make the payment for example (I know which PayInStore additional fee is over the order total but this is  another issue).
The problem: if I place a negative value in additional fee this is not showed and computed before the payment confirmation.
Only a positive value is computed.
Exists a way to make a negative value be computed?
How to make the fee be applied over the order subtotal?
Sorry by excessive explanation but I'm a newbie in nopCommerce and ecommerce.