5

The chip appears to be a ESP-WROOM-02

Unfortunatly, I’ve never had much luck with esptool, and much prefer to work with the Arduino IDE, so can’t really help you.
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When I re-flashed my 3 relay board (shop bought a few years ago), I found it easier to start from scratch and build in features that I needed, and it was a great learning experience - especially as it was just the second time I’d touched a ESP8266.

The designer - Martin Harizanov is usually very helpful, and can be contacted here.

Paul