Thank you so much for your reply. I have done it, but then the checkout button disappear and don't let me go to the bank's site.
The bankers have told me that I have to collect the total amount in a session variable stating the * 100 and then write it on a hidden form element.
The problem is that I need to pass an entire unformatted number for the bank site to recognize it. I don't know if this may help you understand the problem.
Please help me.
Thank you so much and regards,