Well, that's progress!
So, you are trying to column-bind objects of different lengths. Have you tried simply creating each of the objects outside of the column-binding step? Maybe like this?
n <- nrow(playlistURI)
PlayListID <- playlistURI[,2]
Musician <- playlistURI[,1]
PlayListSong <- sapply(seq_len(n), function(i) getPlaylistSongs("Spotify", playlistURI[,2], token = spotifyToken)
length(PlayListID)
length(Musician)
length(PlayListSong)
Perhaps that will provide a clue?
Ben