Esp8266 no serial prints / connecting to WiFi and MQTT Broker problem

[Deva_Rishi]

@bubuq

What value for GPIO4? 2 or 4? beacuase it's digital pin 2 (D2) but it has GPIO4. ;/

'4'
or you can reference it as 'D2'

@bubuq

If I got e.g. GPIO01 (TX) I got defined it like: int led = 1 because it is GPIO01?

Yes that is correct.