Sales Order Down Payment process

Hello SD Experts,

I have a requirement to create a sales order down payment process in my project.

The requirement goes like this:

Sales order is Created and the down payment is due immediately->customer pays the down payment->Down payment is cleared->Delivery is made w.r.t the sales order->FINAL INVOICE W.R.T DELIVERY.

Now, we are using the billing plan 01->mile stone rental.

AZWR condition type and the regular process of down payment.

However, the problem is the final invoice is also required to be created w.r.t the sales order. Whereas, the client wants is w.r.t delivery.

Can someone help me in this? Thanks!