Payment Module add extra fee to total ammount

[01generator]

Hello, 

 

I have created a payment module for prestashop and a local bank. 

All works well. 

After customer demand I want to add extra fee.

I added the precentage that the bank charges and an option if the eshop wants to charge it self or the customer.

On payment selection I have added a message that informs the user that he/she will be charged extra according to his/her total order.

The user pays and all works well.

 

Where is the problem? When I go to back office to watch my order, it is marked with Payment Error State and a Warning message in payment div. (See attachment)

 

How can i add that extra fee to the total ammount of the order? 

 

Thank you in advance.