Sometimes errors, typos for example, are reported in multiple locations but the correction is elsewhere. ... That means I’d expect a source code for ab Arduino project to be like 100 kB at most.

Once you’ve got the basic connectivity to your Home Assistant instance working, there are many code examples in the arduino-home-assistant GitHub page to give you a helping start to connect ...

Luckily, Arduino’s own cloud services make it surprisingly easy to code for the Oplà. I opened the box, plugged the board into the Carrier, and then connected the board to my computer.