

I did some testing, it looks like the auto generated “Liked Music” playlist doesn’t have a proper URL that can point to the music.
A workaround seems to be adding the playlist to the queue, then saving the queue to a new playlist, and using that new playlist URL.
That way you can remove the “music.” part from the “music.youtube.com” and use it like a regular YouTube playlist.
If that doesn’t work for you it might be a DRM issue with how your phone is attempting to download the data. I used my desktop.
It’s the playlist link that’s the problem. It ends with
playlist?list=LM
which stands for “Liked Music”. The downloader doesn’t know your account’s liked music playlist. It needs a playlist ID likeplaylist?list=PLO7q4X25LQEEyJAQe5EEwJxUCSKvuKbok
Basically you need the songs to be in a different playlist