I recognize how essential to reflect the holiday hours of your employees on their payslips for transparency and accurate recording, Emily. Allow me to share some information on why this item won't show in your pay stub.
There are two main reasons for this. Firstly is the set up of your holiday hours. When you add this item as a new pay type, you also need to enter the Rate and tick the Show in Pay Run box from the Pay Rates section before saving it.

Lastly, ensure that the payroll date or range you run is correct. This means that this item is approved and created during these periods.
Additionally, if you want to be certain that the payroll you pull up is error-free, consider visiting this article to learn how can you be notified promptly: Set up pay run warnings in QuickBooks Online Advanced Payroll.
Feel free to return here if you have follow-up questions after following the suggestions above or any queries about generating payslips. I'll always be here to help you. Have a great day!