Have managed to get this fixed,  was playing music to one of my rooms using tidal (airplay).  Using the airplay function at the bottom of the screen I went to add an addional room.  This opens the Sonos app and seemed ato add Tidal to it,   That's not how it supposed to work, but anyway, I got my result 

Thanks for your ‘fix’ Peterjclarke which gave me a great hint.

I also could not add Tidal as a service to Sonos; same symptoms as Peterjclarke describes/shows above.

This is what I did and Tidal is now added as a service to Sonos………

• played a music track on my iPhone via Tidal
• Transferred the sound to my Sonos speaker via airplay button in Tidal
• Whilst music was still playing (now on Sonos), tried adding Tidal as a service to Sonos
• When promoted to do so, sucessfully authenticated Tidal with my logon&(saved)password; also when promoted gave Tidal a friendly name on Sonos and made it my preferred music source so it is shown top of list of services when searching/selecting.
• went back to Sonos and voila! Tidal was there at top of services list
• hope this is useful for others
• SONOS-you need to get your ‘add service’ function in the new app to work very urgently.

Creative solution, @home crispin 

Glad you sorted it out, in a similar way to me.  But it is a case of trying different things until you get a result.  It's a shame.  The most important / fundamental functions of the app are setting up and configuring your system.  If there is one function that absolutely must work that is it.  Once it is set up you can can do most  things though AirPlay and not have to rely on the app.    This is very bad form by Sonos, and is a disincentive to buy more gear from them.  ( yes I'm writing this for the Sonos team to see, and get a sense of what their customers are thinking)