Receivable, in this money sense, describes something that is waiting to be paid to you. A receivable invoice is one a customer still owes. In business English it is almost always about money coming in, not about whether you “can receive” a package — though the pieces receive + -able originally just meant “able to be received.” Accountants talk about accounts receivable: the pile of bills other people have not paid you yet. As an adjective it is office-like and a bit formal. You would not call a birthday present receivable. Though actually, receivable money is still only a promise until it arrives; it is not cash in the bank.