Thank you for posting in the Community. I'd be happy to help share some details on how to set up a payroll item to show in Box 12 with Code L on the W-2.
The amounts that appear on tax forms depend on the tax tracking type used in a payroll item. To make sure the tax tracking type is correct, I recommend consulting with your accountant.
Once you know the tax tracking type, you can create the payroll item. Let me show you how:
From the QuickBooks Lists menu at the top, then select Payroll Item List.
At the lower left corner, click Payroll Item then select New.
Select Custom Setup then Next.
Select Addition then click Next.
Enter the necessary information like the Payroll Item Name, the Liability/Expense Account associated with the item, Tax tracking type, How to Calculate the item, and/or Default Rates and Limits (Rates and Limits entered here will affect all employees).