And how is your hardware wired?
Does this mean that ZCD is connected to the NodeMCU pin labelled D3 (GPIO0), or GPIO3 (the pin labelled Rx)?
If it’s the first, then that’s not a good choice of pin and could prevent your NodeMCU from booting. See this thread for more info:
If it’s the latter then it’s going to prevent you from using the the serial monitor for debugging, which will be a drawback.
I take it that you don’t want to share your code?
Pete.