How to get payment due in payment module?

Hi everyone :-)

Many customers requested for a monthly installment plan and there isnt any add on yet to do so :-( . So i guess I have make a temporary solution for installment plan and do it manually till an add on surface. I am trying to capture the payment due to be used as calculation in a payment module but without any success. Is it possible ? Any idea how to capture it ?

Or am i doing it all wrong, lol ? Kindly let me know

Thank you and have a nice day :-)
The order total does not exist at the time payment options are shown. Only the cart total and the shipping fee can be accessed. This is because payment fee is part of the calculation of the total. A customer must select a payment option before an order total can be calculated.

It does exist when transfer() is executed so you could create a payment window by returning HTML that lets the customer confirm the amounts. See the wiki article how to create a payment module and return HTML in transfer().
Thank you for your reply :-)