So that almost worked, inasmuch as I used the nvm method to get the correct version of nodejs and the manual invocation all worked. As soon as I tried to run the systemd service as described it all failed (I couldn’t connect to the web server o9n the Rasp Pi). What I did was to change the plexamp.service file to use the nvm-specified version explicitly in the ExecStart statement, rather than the /usr/bin/node path:

ExecStart=/home/<user>/.nvm/versions/node/v16.20.2/bin/node /home/<user>/plexamp/js/index.js

That seems to have got plexamp running correctly after a reboot on the headless Rasp Pi.

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