seems more people requested this. As I don;t have the hardware its dangerous to tell you what to do.
You can try to reach out to the author
Or if you want to take a walk on the wild side, I’ll take no ownership or support if it goes wrong or even fail your current installation.
sudo apt -y install build-essential
cd ~
wget https://github.com/Saiyato/volumio-audiophonicsonoff-plugin/raw/master/volumio-audiophonicsonoff-plugin.zip
mkdir ./onoff
miniunzip volumio-audiophonicsonoff-plugin.zip -d ./onoff
cd onoff
npm update (it might be possible that this is not even needed)
npm install --save onoff@6.0.0
volumio plugin install
cd ..
rm onoff
rm volumio-audiophonicsonoff-plugin.zip
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).