Please read this support page for further help with Apple SharePlay: Use SharePlay to watch and listen together in FaceTime on iPhone - Apple Support.
"With iOS 15.4 or later, you can start a FaceTime call in the Music app (or other supported music app) and use SharePlay to share the music in sync with others on the call. Each person can use the music controls to pause, rewind, fast-forward, or scrub to a different part of the song. And anyone using SharePlay can add songs to the shared queue. The people you want to share with must have access to the music (for example, through a subscription)."
Please make sure both devices meet the requirements.