A Sales Invoice is generated when a Delivery Note is saved - the Invoice(s) can be found in the invoice list with status created.
You can also create an Invoice manually (generally only used when the automatic generation of invoices when Despatch Notes are created function is turned off)
Navigate to Network⇒Invoice⇒Invoice
Click the New button
This opens the New Invoice page
Select the Customer you are creating the invoice for and then click the Add button
A pop-up window appears displaying all of the delivery notes for the selected customer that have not yet been invoiced. Select the required Delivery Note and press Save
Details from the Delivery Note are then carried across to the new invoice, click Save and the new invoice can then be Printed or Emailed.