What favor does Joker ask Batman in the Telltale series?

Solution 1:

I played through the entire game once again, choosing only those options that I had not chosen in my first playthrough.

I managed to make sure I once again promised to return the favour to Joker.

But, nothing seems to lead me to any actual event where the Joker asks the favour.

I must say that this was a pointless part in the otherwise okay game plot.

EDIT: Or it may be continued in the possible season 2 of the game. Source: Movie Pilot. But a season 2 is not in the works as of now.