new iphone not connecting via sonos app ( no problem via Spotify ditectly)

My iPhone works fine with my Sonos system and Sonos app. But the Sonos app on my wife and daughters New iphones can t find the Sonos systeem.  But playing directly from Spotify or other source works fine!  So there must be some connection between their iPhones and the Sonos system. Resetting the app and wifi and router doesn’t help.  All 3 iPhones in my family have iOS 18. Only mine works well with the Sonos app.