Well, first ZeroBank isn't a bank as the aim is to eliminate the need for centralised organization. If you don't understand the role of shops or taxi drivers, when someone go to their shops or on their taxis, they can receive the money and send somewhere else or give the customers the afore-agreed money via ZeroBank's system. Check out this vedio if you haven't already:  https://www.youtube.com/watch?v=mFYw7MGuw7o&t=126s