Items set to Do Not Bill in ConnectWise PSA will transfer into Quickbooks Online with the quantity applied in ConnectWise PSA. When you look at the Do Not Bill item on the Quickbooks Online Invoice details the amount or cost of the item(s) will be $0.00. The integration will apply the item in Quickbooks Online to ensure inventory is accounted for.
Consider the following screenshot, QuickBooks Online will reduce the inventory by 5 per the invoice details.
Please note that an items costing is handled by QuickBooks Online internally when an item is used on a transaction. You can view this on the transaction journal in Quickbooks Online.