Trade

In the building, there isn't any currency system, and since robots do a good majority of the work there, barely any of the organic life do much service work, too.

When it comes to paying people back for favours and stuff related, I kinda think of it how it would be for siblings that are still living under their parent(s)'s work (from experience). You know, the whole "I do this for you, you do something worth that amount for me back," or some "I got you this, you get me that," sort of negotiation.