Moving playlist from Spotify to Apple Music

Hi all. I need to downsize from having Spotify, Apple Music and Pandora. I was able to move my playlists from Spotify to Apple Music using an app (SongShift) but cannot download them into Apple Music for offline listening even though I am subscribed to Apple Music. I am able to listen to them on Apple Music app but only when connected to the Internet. I do all this through my iPhone 13. Am I missing something here? Thx