Just exchange mySerial by Serial2, that should work.
You need a Serial2.begin() in setup too.
You are aware that Serial2 is the third serial port, not the second?
So the Nextion is connected to pins 16 and 17?
Just exchange mySerial by Serial2, that should work.
You need a Serial2.begin() in setup too.
You are aware that Serial2 is the third serial port, not the second?
So the Nextion is connected to pins 16 and 17?