Why:
An order should be invoiced once all work on it has been completed. An order is considered to be complete once the invoice has been raised and therefore no further amendments can be made to it.
Where:
From the Parts Order View, open the order you want to
invoice. When you've opened the order, select Order from the menu bar
followed by Print > Invoice or select the invoice button 
.
How to Invoice Parts Orders:
When you have selected the print command, a Print Invoice window is displayed, confirm that the delivery dates are correct and click OK.
Select the check box if you want to invoice in an alternative currency. Fusion will then pick up the currency type from the customer profile information.
If the order is a cash sale, check the tick box to confirm payment has been made. This is meant to act as a prompt to remind you to take the cash from the customer! Then click OK.
If prompted for invoice text, you can enter any additional comments that you'd like to see printed on the invoice before clicking OK.
The system will then return you to the parts order view. In the list of orders, you'll notice that the order you just invoiced now has a different icon which denotes that it has been invoiced.
What else would you like to do?
Customer Point of Sale Details.
Finding Out About Gross Profit.
Printing and Re-Picking Slips.