I have a project on Arduino (exapmle Mega 2560 ).
The Arduino should act as a cash receiver and send exactly the amount that I deliver via Bluetooth to the balance. I have a working code, but it only works on a few coffee vending machines. Where it does not work, it blocks everything with one code:
#define CSH_ACK 0x0100 // Acknowledgment, mode bit set.
I also have an insulator circuit.
The fact is that it works on one device. I think my code works on level 1 alone.