conect migrated down payment to sales order

We have migrated a "down payment" from legacy system, in the open items recivables. But can I relate it to a sales document?

In this scenario the customer have recived a down payment from a customer for a project but it is still to be delivered during 2019.

We want ByDesign to automatically keep track of it and not generate a new invoice without deduction of the down payment done. How do we do that?

/Petra