Hey, 

to configure Odoo Sales to invoice a down payment at the time of order and the remaining balance at delivery, follow these steps: First, go to the Sales module and ensure that the options Sales/Configuration/Settings are enabled for Invoice on timesheets and materials and Down Payments. Then, create a sales order in Sales/Orders/Quotations, adding the customer and product details. Once the sales order is confirmed, click on Create Invoice and select Down Payment (percentage) or Down Payment (fixed amount), specifying the percentage or amount for the down payment, and validate the created invoice. To invoice the remaining balance, go to Sales/Orders/Orders and confirm the delivery of the order. After validating the delivery order, return to the sales order and create the final invoice by selecting Regular Invoice to invoice the remaining balance, and then validate the final invoice. Following these steps will allow you to manage the invoicing of down payments at the order stage and the remaining balance upon delivery efficiently in Odoo.

Hope it helps!