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Thanks for keeping me posted. Can you check if the issue occurs on other devices when you log in to the new account? Also, could you try with another network to see if there are any changes?
Keep me posted.
I tried adding the song when I was on a different network, and got the same message. I'm not sure how to access my playlist and add songs on a computer.
Update - I accessed my playlist on my computer, and tried to add those songs to my playlist, and got the same message!