@kebson Thinking about your message, I assume that you connected the collector of the transistor to GND and control the relay though through the Vcc & GND pins of that relay board. Two topics are to be discussed: Current draw. According to the data sheet, the coil resistance is 70 Ohm, resulting in an current of 47 mA at 3.3V. At that load, the output voltage should be lower than 3.3 V, so it might "just" fit. At about 3V, the force at the relay contacts may be lower than at 5V, causing higher relay contact wear. Flyback voltage peaks. If you did not remove the flyback diode from the board, that might work, at least for a while. But still I would not consider to connect an inductive load directly to the ESP32 output pins. It may work for a while, but then break. B.T.W.: What is the mains voltage/power of the Pump?

@jiancha For the input of the Lopy Youll need some kind of Pull-up. That could be an internal pull.-up resistor, or an external one, like 4k7 to 3.3V. Otherwise the input is floating when the switch is open. Which Pin of LoPy are you using for input, and how do you control it? Using the reed relay is in principle a good idea to protect the Lopy from transitions. But the values of 33k/100k for the voltage divider are also suitable. The resistor values are not too high. The input resistance of the Lopy is several MOhm.

I suggest to use this Pycom LoRa-Mac nano-gateway to start with : LoPy Nano-Gateway Extended (Timeout and Retry) It was a development from the earlier version : LoPy Nano-Gateway

@kots Even it that is true, it does not sound reasonable. G2 is used for the REPL communication. You might use another GPIO port for switching, but G2 seems to be an odd choice, as well as driving a step-up converter power input with a GPIO port, especially if a single transistor switch or digital gate is sufficient for the purpose.