Billing/Flat-Rate Price Contracts Settlement using down payment processing is only possible if in Customizing for
Financial Accounting
you have set the correct field status for the additional account assignment. For more information, see
Billing with Down Payment Processing
.
In a flat-rate contract, you invoice on the basis of the sales order.

You can create a customer payment plan using the billing plan stored in the sales order. Down payments, partial invoices, and the final invoice are either related to a milestone or the correct accounting period.
The system determines the value to be invoiced from the item condition records or from the exact dates in the billing plan. In milestone billing you can specify the percentages or amounts to be invoiced.

After you have created one or more down payment request(s) and partial invoice(s), the sales order is given the following: