Unable to find a device! Please add a device to continue...

[debian1500]

I get this output:

    $$$$$$\$$$$\   $$$$$$\  $$$$$$$\  $$$$$$$$\ $$$$$$\  $$$$$$$\   $$$$$$\
    $$  _$$  _$$\  \____$$\ $$  __$$\ \____$$  |\____$$\ $$  __$$\  \____$$\
    $$ / $$ / $$ | $$$$$$$ |$$ |  $$ |  $$$$ _/ $$$$$$$ |$$ |  $$ | $$$$$$$ |
    $$ | $$ | $$ |$$  __$$ |$$ |  $$ | $$  _/  $$  __$$ |$$ |  $$ |$$  __$$ |
    $$ | $$ | $$ |\$$$$$$$ |$$ |  $$ |$$$$$$$$\\$$$$$$$ |$$ |  $$ |\$$$$$$$ |
    \__| \__| \__| \_______|\__|  \__|\________|\_______|\__|  \__| \_______|

                        ──── Apple Music Downloader ────


[22:53:38] [ManzanaCore] INFO: Loading device...
[22:53:38] [ManzanaCore] ERROR: Unable to find a device! Please add a device to continue...

Which device it asks for?

[debian1500]

Please

[chad-fa]

It must be late reply, but I stumbled upon the same problem. It took me two days to figure this out having no Linux experience whatsoever, so here is the solution:
As clearly stated in Manzana's readme, device is a term for the Widevine device files. Long story short, this are the keys generated by DRM-compatible device which are created during streaming of DRM-protected content (such as Apple Music).
Just follow this instruction to obtain required files using Android Studio developer tools. Once you succeed, put them to %path-to-manzana%/device/ and you are all set!
Next obstacle you might find would be mediaUserToken. This value is found in cookie files generated by your browser. In order to obtain it, you must login to web version of Apple Music using your credentials (it goes without saying that you should have an active subscription) in cookie-enabled session, then extract it by any mean of your choice. I used this convenient tool.
Much thanks to @dropcreations and @loveyoursupport for this great piece of software. Cheers.

[elhackman]

Just in case, this is another set of instructions https://github.com/FoxRefire/wvg/wiki/How-to-dump-CDM-key-pair-from-AVD