Music not playing through Apple Watch

Having purchased my Apple Watch (9) a few months back, I was initially able to play music from iTunes and from Spotify (having added the app to my watch), through my Apple Watch, being given an icon option to choose either my Apple Watch or my iPhone when initiating the music on my watch, for the tracks to play through.

A couple of weeks back, this facility and these options stopped functioning, and now I'm on able to choose my iPhone to play music through, so I'll press play on my watch, but the music will play through my phone, and I'll have no way of changing this.

I have tried all avenues to adjust this and re-establish the previous facility/option, but nothing has worked.

Please advise?

Many thanks in advance, Glynn Reed.