I would to expose this business process looking for some advice:
* Customer advance some cash for future payables of invoices billed to him, but payed by the service organization, it does not have consideration of down payment.
* Sometimes the balance of this advance and payables are positive or negative, in any case the service organization can decide whether to include them on final professional service invoice or not (or partially).
How could we achieve this business process in a customer project?
Thanks in advance.