Why do I keep getting this error message. I also downloaded a ton of music last week on this phone. Where is my music going?

Sign out of the iTunes Store and then sign back in.

In settings - Music - Turn off iCloud Music Library and then turn it back onand Turn on “Show Apple Music”

Check other settings:

Settings > Music > Optimize Storage and be sure the option to Optimize Storage is disabled - if you don’t want this 

• Also check if you have enough storage space:

How to check the storage on your iPhone, iPad, and iPod touch