Hi, my name is Daniel.
I have experience in microcontroller <-> Android communication via Bluetooth (both ble and classic). Also I have experience to develop android Service (that runs in the background) that uses Bluetooth, so you don't have to have the GUI opened everytime when you want your application connects to Arduino. In my past projects I used Bluetooth on ESP32 and HC-05 / HC-06 modules for Arduino.
Could you please elaborate more about your Arduino configuration and which module do you use?
I work in a close communication with the customer, so you'll be involved in a process, if something you would like to add or customize in the process, no problem.
Thanks,
Daniel