This article will show you how to associate POS Screens with the Catalog Tab that displays your merchandise. You will want to associate POS Screens with the Merchandise tab so that POS Items can display on the tab within specific categories.
Instructions
Navigate to Configuration > Public View > Catalog Tabs
Edit the Catalog Tab that is your Merchandise tab (frequently your POS tab)
Use the Merchandise on Tab dropdown to select your POS Screens (or All Screens)
Click Save Catalog Tab