All ESP8266 boards running MicroPython.
Official boards are the Adafruit Huzzah and Feather boards.
Target audience: MicroPython users with an ESP8266 board.
So at least I can see, that is is "normal" level, and the ESP8266 should be able to receive it. But you still do not know, whether any data is actually exchanged.
Yep, still trying to understand what I'm doing wrong
Anyway, thank you for your help Roberthh
Hope I'll solve it. Then the solution will be posted here.