After spending hours in a loop of re-authorise / log into your Sonos account misery I resorted to deleting Sonos and ITunes apps from my phone (iPhone 15) / reset my Sonos speakers and started over. I downloaded the Sonos app, connected the speakers and then the WiFi. I was then able to add back my iTunes account. It took 15 minutes!
I couldn’t find any helpful suggestions online so resorted to a complete reset - it worked but surely shouldn’t be this hard!