Sadly the first one comes too late for you: Do not do factory resets unless directed to by Sonos as they usually make a problem worse. (just mentioned as a warning to other folks)

Your profile says you only have the one Sonos One so I’m confused about the “add to my system” you mentioned. Do you have other Sonos or can you explain just what you are trying to add it to?

Thanks for the reply Stanley, the secret was to update the app from within the app. It must ‘remember’ serial numbers of products that have been registered? Found this out via Sonos tech chat. Anyways, all working now. Thanks. David