Did you just update your iOS recently? If so, the update probably just logged you out of the Sonos app. If you log in and perform Trueplay again, it probably won’t ask you again.

@GuitarSuperstar Have had several iOS updates over the 3 year period of owning Sonos, but never had to log in. Just had another iOS update ..logged in after completing. I’ll see if it asks again in the future. Thanks for your reply. 

I think Trueplay is an “admin-level” setting to stop randos messing with your system. Hence the login requirement.