Apple music Sync Library Not Enabled

Syncing iPhone and Apple Music - When I turn sync, it appears to be trying and then turns syncing off and I get the following comment:

Sync libary not enabled.  Syncing Libraries would put you over the song limit.  delete music from this iphone and try again or delete the other library and replace it with this one.

im trying in 2 different iPhones.

What do i do? Now i can’t download music.

please help!