Unable to add music to Apple Watch

I'm a long term user of Apple Watch. Currently using Apple Watch SE (watchOS 10.4) and iPhone SE (iOS 17.4.1).

I've been able to add music to Apple Watch for years without a problem.

Now I am unable to do so. I've followed instructions at Add music to Apple Watch – Apple Support (UK) also unpaired and paired watch.

I am able to go into 'Music' on watch. I'm am then able to click 'Add Music..'

I get the message: 'Your music will download soon.'

I then see the 'wheel' for about a minute.

Then the music I have tried to add disappears from the screen.