Tried it, didn't work

[shillshocked]

Set up as described in the extra help. After setup:

dbus-send --print-reply --type=method_call --dest=org.mpris.MediaPlayer2.spotpris.device5d81cefb30a5337f5dcd7af052f3a1b0fc1935c3 /org/mpris/MediaPlayer2 org.freedesktop.DBus.Properties.Get string:org.mpris.MediaPlayer2.Player string:Volume

Error org.freedesktop.DBus.Error.ServiceUnknown: The name org.mpris.MediaPlayer2.spotpris.device5d81cefb30a5337f5dcd7af052f3a1b0fc1935c3 was not provided by any .service files

[AndydeCleyre]

What's the "extra help?"

What does playerctl -l show? playerctl

Is spotify actively playing something (not paused?)

Is there any output from the spotpris2 process?

[shillshocked]

Spotify shows up in playerctl. I can use sp and other tools with it no problem. It's running in memory, but frozen with no output. Doesn't matter if something is playing or not.

[AndydeCleyre]

What's the "extra help?"

What does playerctl -l show?

[shillshocked]

spotify
chromium.instance1286

[AndydeCleyre]

It looks like playerctl is not seeing spotpris2 -- so where did you get that device name from (device5d81cefb30a5337f5dcd7af052f3a1b0fc1935c3)?

Can you try making this change, to see if you're really being affected by #8 here? I'd guess it's not that, since you don't have any error output, but it's still worth a check.