Found out the problem: old firmware or somehow wrong firmware was fetched with
$ git clone GitHub - openenergymonitor/EmonESP: ESP8266 WIFI serial to emoncms link
when I followed the guide from EmonESP/readme.md at master · openenergymonitor/EmonESP · GitHub
I downloaded the ESP 2.3.0 source from Github, put it on my home folder, edited src\src.ino file as stated on earlier messages (Serialbegin 115200 → 9600). And then uploaded it as in the instructions in the guide.
Now I receive data from EmonTX to EmonESP login page “Latest Data”.
Thanks Robert and Simsala for your kind help!