The CashApp QR code on the POS client-screen is pretty much everything you need. Almost there!
Discussion
There's a handful of lightning apps that have a "POS system" but they're not quite there and are only good for mom and pop shops.
For example, you can't lock settings from employees and it doesn't integrate with inventory management. There's also the issue of syncing with your fiat payment provider. Otherwise you have to reconcile inventory each night in two separate systems then merge them manually.
Ripe for innovation. Sounds like your head is in the right place my friend.