POS Menu (/admin/menus/pos) is a day-by-day calendar where you decide which meals from your recipe catalog are available to sell through the POS Menu ordering module, per delivery date — the same association screen used for Grab & Go / Catering / Real-Time menus, just filtered to the "pos" menu type. POS Categories is a separate, unrelated setup screen that only controls how those meals get grouped into tabs on the selling screen. You need POS Menu items scheduled before there's anything for the POS Categories tabs to filter.