A large-format display, not a tablet glued to the front of a box
The screen on an advertising vending machine is a large-format commercial-grade HD display engineered to work in high-traffic environments: visible from a distance, readable in varying light conditions, and built to run 24 hours a day without degradation. This is the real estate the advertising business runs on. The bigger and clearer the screen, the more valuable the advertising inventory, and the same display carries your full product menu during every customer interaction.
Content performs at the point of attention. People approaching a vending machine are at the highest moment of purchasing attention in any location. Their eyes are on the machine and their wallet is already coming out. That is the moment the screen reaches an audience, not as background noise, but as the primary visual focus. Product revenue runs exactly as it would from any standard machine. Nothing changes on the product side, and the advertising stream runs on top of it.

