It is recommended to create an invoice from a delivery.
Go to Orders" - "Delivery". 
Click on the "Despatch advice number" for the delivery to be invoiced. 
Click "Create invoice draft". 
A pop-up window appears. 
Click "Create new invoice draft". 
A new pop-up window appears. 
Click, and enter a "New invoice number". 
Click "OK". 
An "Invoice draft" will be created. 