We decided to focus on cafeteria and lunch restaurants where transactions should be as fast and frictionless as possible. By using your feet (or other body parts) to pay instead of hands you can fly through serving lines. We used Raspberry Pi with RFID reader and Neopixel LED strip to simulate point of sale. Successful transaction triggers Android push-notification through Ionic framework (Angular) or sends an SMS message (46elks API).
Based on examples and dependent on packages from here: poplatek/junction18-public