A proforma invoice shows a buyer what the final invoice will look like, before the goods ship or the work starts. It is often used for advance payments, imports and purchase approvals.
A proforma looks like an invoice but it is sent before the sale is final. It is a statement of what you intend to charge, and it is normally not the document you record the sale with.
When the order is confirmed or delivered, use “Make an invoice”. The invoice gets its own number from your invoice series.