POS integration connects the screens to the till system, so what a customer reads on the wall comes from the same source as what they are charged. In practice that means prices, availability and sometimes queue state.
It removes the most damaging content error in retail and hospitality: a screen advertising something at a price the till disagrees with, or promoting an item that sold out at lunchtime. Both are ordinary consequences of maintaining prices in two systems, and both cost trust at the counter.
The caveat is that POS systems are the most conservative software in the building, and for good reason. Many are old, many are certified for payment handling, and their operators are correctly reluctant to expose them. Expect a read-only export or a middleware layer rather than a live API, and design around a periodic sync rather than instant updates.
Decide explicitly what a screen shows when the sync is stale. Hiding a price is recoverable; displaying a wrong one is a dispute.