Lightspeed work orders have a very specific behavior when it comes to inventory management:
As soon as an inventoried item is added to a work order, the corresponding inventory is immediately removed (thus reserving the product)
As a consequence, when invoicing a work order, QuoteMachine no longer has to remove inventory at the time the invoice is created. To prevent affecting the inventory, the invoice generated by QuoteMachine is composed of miscellaneous non-inventoried items having the same name and price as the ones that were added to the work order.
When the work order is invoiced in QuoteMachine, the work order total is modified to indicate there is no remaining balance left to pay on the work order (the balance is born by the QuoteMachine invoice).
The work order balance is modified by the addition of a line with a negative amount.
To ensure the overall profit margin is correct despite the duplication of items between the Lightspeed Work Order and the QuoteMachine invoice:
Line items on the QuoteMachine Invoice have a $0 cost.
Line items on the Lightspeed work order bear the actual product cost.
Checking out work orders
Checking out work orders, even if they show a $0 total is useful as it will flag the inventoried items as sold and will update the reports accordingly in Lightspeed.
Invoicing Lightspeed work orders with QuoteMachine creates lots of entries in Lightspeed which does not always "feel natural" when looking at reports. QuoteMachine operates this way according to Lightspeed's Application Programming Interface (API).
If you're using work orders without having any "labor" to manage. You probably should consider using QuoteMachine's sales order feature in replacement. It offers a cleaner, flexible workflow, fully integrated with Lightspeed Retail.