Kiosk Software for Perfume Vending Machine (Nayax, Hardware Control, UI)

Project Overview: I am looking for an experienced IoT/Vending software developer to build a lightweight, custom kiosk application for a perfume vending machine. I want to replace the current heavy software with a clean, reliable solution. The system must handle a UI with an ad-screensaver, communicate with a Nayax cashless payment terminal, and control hardware (relays, physical button, LED). Hardware Setup (Fixed): Mainboard / Computing Unit: The hardware is already built into the machine (originally manufactured in China) and cannot be replaced. The exact board and operating system are currently unknown to me. You must be able to work with this existing hardware (reverse engineer/adapt) and guide me to identify the exact specs. Payment Terminal: Nayax (Integration via MDB protocol or Nayax API). Actuators/Inputs: 5 Relays (for 5 perfume pumps), 1 physical push button, 1 LED inside the button. Display: Touchscreen. User Flow (State Machine): Screensaver: Display plays a continuous loop of short .mp4 videos and .jpg/.png photos stored locally. Wake-up: User touches the screen. The screensaver stops immediately, and a UI with 5 scent options appears. Selection & Payment: User selects 1 of the 5 scents. The software sends the corresponding price to the Nayax terminal. Authorization: Once the Nayax terminal confirms successful payment, the software turns ON the LED inside the physical push button. Dispensing: The user presses the physical button. The software registers the input, turns OFF the LED, and triggers the specific relay (1 out of 5) associated with the chosen scent for exactly X seconds. Reset: A short "Thank You" screen is shown, and the system returns to the screensaver loop. Software & Remote Requirements: Tech Stack: Must run smoothly and stable on the existing hardware in a locked Kiosk Mode. Remote Access: Must include a secure remote setup via a 4G/WiFi connection so I can access the system remotely. Admin Dashboard: A very simple local web interface (accessible remotely) to: Check basic stats (e.g., how many vends per scent). Upload/delete ad media (videos/photos) for the screensaver without physical access. Trigger a system reboot. Milestones (Fixed Price - Let me know your quote): Frontend UI (Screensaver, Selection Menu, Admin Dashboard) Hardware Control on existing board (Relays, Button, LED) Nayax Payment Integration (MDB/API) Final setup (Auto-start on boot, remote access config, testing) Please start your proposal with the word "VENDING" so I know you read the full description. Please also briefly state your experience with Nayax payment integration and working with pre-existing vending hardware.