How to show an advance payment discount on a commercial invoice?

Advance payment in international trade defined as a payment that is made ahead of shipment take place, such as importers are paying for whole or part of the goods value before they actually receive them. 

Sometimes exporters and importers agree on an advance payments, which will be taking place ahead of the shipments. 

These kinds of advance payments should be demanded via proforma invoices and the advance payment amount must be shown as a discount on the commercial invoices.

On this page I will try to explain how to show an advance payment discount on a commercial invoice.