To use GPIO shutdown for the Raspberry Pi, add following lines in the file /boot/config.txt
edit file: sudo nano /boot/config.txt

# signal power off with green led
dtoverlay=gpio-poweroff,gpiopin=16

# shutdown Pi when joystick button is pressed
dtoverlay=gpio-shutdown,gpio_pin=26,gpio-pull=up

# shutdown Pi when GPIO GP0 on Hat is set to low
dtoverlay=gpio-shutdown,gpio_pin=17