Hello
I have the same device and I asked audiophonics for this plugin. For the moment, the plugin is not working, but they proposed to edit some configuration files so you can invoke directly a dtoverlay and have 90% of the functionality of the power manager without using a plugin or installing anything. Just add these two lines in /boot/userconfig.txt:
dtoverlay=gpio-poweroff,gpiopin=22,active_low
dtoverlay=gpio-shutdown,gpio_pin=17,active_low=0,gpio_pull=down
and the power manager should be functional on the next reboot. This method works on almost any system running on Raspberry Pi (but does not react to reboot / poweroff initiated from another source than the on/off button).
Christian