In QuickBooks, Click on Edit > Preferences > Set the Unit

This Document defines how to setup UOM with T-HUB and QuickBooks
Enterprise (Note this is not supported for QuickBooks Point of Sale)
In QuickBooks, Click on Edit > Preferences > Set the Unit of Measure to
Multiple U/M Per Item
Picture : 1
In QuickBooks, Click on U/M Set List
Picture : 2
Define the Unit of Measure SET details. Set the default Unit name to
use for Sales. In this example it is Case (which contains 20 count of
each)
Picture : 3
Assign the Set name for the Item in QuickBooks Item List
Picture : 4
In T-HUB, Edit Store Preferences > QuickBooks Settings > Item Settings,
Check the flag for Set Unit of Measure for items Sold.
Picture : 5
Once you have all the above setup, then T-HUB will assign the default
Unit of Measure to Item when posting to QuickBooks.
So now lets say there is an order for Item named "intelc2d" with
Quantity of 5 (Picture : 4). Now T-HUB will post this sales to
QuickBooks with Unit of Measure as Case and quantity of 5. In other
words 5 quantity of case Unit.
Please note that all sales for item "intelc2d" will be posted to
QuickBooks with the same Unit of Measure as Case. In other words you
cannot have one order posted to QuickBooks with UOM as Case and
another order with same item posted with UOM named Pack