Thanks for coming to the community for help. Liked Songs isn't treated as a playlist. What you can do, as a workaround in this case, is call the Get User's Saved Tracks endpoint (the limit for this is maximum 50 tracks per page) and use the Start/Resume a User's Playback endpoint to play those tracks.
If this is something you'd like to see, I recommend creating a new idea on the Spotify Community. That way, Spotify can keep track of it.
Let me know if you have any questions!
Have a good one,
HuboRock Star 16
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