Odoo 15 introduced the settlement of quotations and orders. This works fine when orders are still in quotation status or when deliveries have not been done yet. The problem is when the deliveries have been done, but the payment is not made yet. 

When an order line is already delivered the quantities transferred to POS will be reduced with the delivered quantities and thus reducing the order total to zero (in case of full delivery). 

Example steps:

1. create Sale Order in Sales 
2. Add storable item to order lines
3. Confirm the order 
4. Odoo create the deliveries
5. Deliver the order (all deliveries are now done)
6. Go to POS and click Quotation/Order button, find your order 
7. Click Settle the Order
8. Notice the items are transferred to POS, but quantities are set to zero (actually qty minus delivered qty)

It gets especially confusing for shop personnel  when the order contains service items and storable items: only the not delivered and the service items can be paid. The order will be paid, but there will be a remaining amount for the items already delivered. So at this point the customer must pay an invoice too. 

So to prevent this, this order should be paid from the Invoice app. But shop personnel have no easy way of spotting this beforehand, they need to utilize 2 apps (Sales and POS) in order to determine the best way to receive the payment... is this intended functionality?

How do we use the Quotation/Order functionality for already delivered order lines?