I just installed it. You don't upload the original included ibank.php but the one from Christianb. So replace the original ibank.php before installing.
Then upload ibank.php and then import the original product file. Works nice.
Suggestion for the future: would be nice if there would be another option to have a certain "forums main saldo" a bit like a real bank from which users also can loan money for a certain percentage of interest.

This way you can also limit the total amount of money which can be loaned, when forumsbank has no money, no loan is possible.
This could be expanded with an option like max amount of money possible per user to loan or things like that.