Custom code when saving transaction id

Hello

Im working on extending HikaShop a bit.
Im trying to locate the code that deals with epay credit card payment.

What i wanna know are following:
Where is the code that contacts epays terminal?
Where is the code that handles the response array from epay?

I need to add a parameter to epays terminal url (subscription=1) so that it returns a subscription id aswell in the response array from epay.
I need this so i can save in it a table and use it for later subscription payments in a Mobile Web App.

I have been searching through tons of files for HikaShop but nowhere have ive been able to locate the Epay payment part.. Is it a part of the bluepaid plugin?

Looking forward to hear from you

That makes sence and i also read that in the developer documentation. But when i looked in that folder from my PHP Editor (NetBeans) it was all empty.
I just double checked with FTP client and the files shows up
Now i just need to figure out why the files are not showing up in NetBeans haha

Thank you!