Hi there twoclrsnmyhead,
We understand you're seeing an error alert when trying to play songs offline in Apple Music on your iPhone. We appreciate you taking the time to connect with us here in Apple Support Communities, and we'd like to learn more to see how we can help.
Are you unable to play any songs offline or is this only happening with some of your downloaded songs? If this only happens with some of the downloaded songs, let's try removing and redownloading them to see if that resolves the issue. Learn more from the links below:
Delete music, movies, and TV shows from your device
Redownload music
Also, iOS 14.7.1 was recently released and you may want to update to see if that helps. If needed, this support article provides step-by-step instructions for updating your iPhone:
Update your iPhone, iPad, or iPod touch
Let us know how it goes.
Cheers.