This came up with regard to a leasing software application. Occasionally lump sum payments must be made and the reasons the payments were made - i.e., the object paid for - must be documented. I don't know what to call those objects. Payment object sounds more like the currency used for the payment. Payment Subject is a possibility but seems pretty vague.
Examples of the things that the lump sum payments can cover are Property Tax, Renovations/repairs, property signs. These could be viewed as additional costs indirectly associated with the leasing arrangement. That help any? (Thanks for your inputs so far ... altho not quite in synch with the need yet.)