Why are my purchased songs showing "Unauthorized Content" on Apple Music?

I had an active Apple Music subscription. While it was active, I added some songs to playlists using the subscription, but I also purchased some music on iTunes, knowing I was not going to renew the Apple Music Subscription. The problem is, all the music that I purchased now has a "unauthorized content" message and only plays the first 15 seconds of the song. The full songs that I purchased will play on my Macbook Pro, but not on my iPhone. I have already restarted the phone and signed out and back in of my "Media and Purchases" Apple ID account, and it hasn't worked. The only thing that has worked is deleting the music I purchased and re-downloading them, one by one. But it's too many songs. That would be too tedious and time consuming to do. I paid for the songs, why won't they play on my iPhone?

[Re-Titled by Moderator]