Hi Jeanette
Try removing your watch from the charger and then restarting both your iPhone and your watch. Turn both devices off first, then restart your iPhone before restarting your watch:
- To turn your watch off: press and hold the side button until you see the Power Off slider; drag the slider to turn off.
- To turn it back on: press and hold the side button until you see the Apple logo.
Check also that:
- All music within the playlist to be synced is already on your iPhone and does not first need to be downloaded from the cloud (eg Apple Music).
- Your watch is still paired with Bluetooth headphones (on your watch: Home screen > Settings > Bluetooth).
More information: Listen to music on your Apple Watch - Apple Support