Without going into too much detail this is the background:
Prestashop built to create a Purchase Order
Purchase Order is then emailed to sales staff
Sales staff creates the order on internal system, is sent to warehouse picked and packed
At the end of the day the order is then required to be uploaded BACK to prestashop - so the invoice
So my question:
What is the best way or if someone has done this already for importing XML OR CSV files that contain invoices for an order and then assigning them to the correct id so the customer can access them via the web admin.
Any advice?