Arduino MKR Zero problem with new UART comunication

Hardware MKR Family MKRZero
1

Hi everyone,
I'm new to the Arduino community!

I'm currently using an Arduino MKR Zero board and I need to add a new communication because the Serial1 on pins 13 and 14 is already used by another device.

I've followed this tutorial from Arduino official website to create a new serial communication, but using the given code I have no communication on pins 0 and 1.

The code compiles, but it doesn't work when uploaded to the MKR Zero board. I've noted that IrqHandler() is not highlighted in my Arduino IDE (it remains black).

So, should I install some library?

Thank you.