Unable to play/airplay from iPhone 15 to stereo pair of HomePod minis

Having reset my minis a few times in order to clear the problem, I still cannot play from iPad or iPhone to the pair of minis. When trying to play from (say) Apple Music to the minis, the play icon is greyed out. Also when paired and unpaired with Apple TV. When resetting there was a screen flash stating that because my router is not allowing airplay etc. however I have a Mini in another room which is playing as it should and there is only one network in my household, so I doubt the validity of the screen flash.