I’ve been banging my head against a brick wall trying to setup a new Sonos system in my RV using two Sonos Roams. I already have a home system (two Sonos Beams & four Sonos Ones) and have connected to a separate system at work (two Sonos Fives) so thought it would be no bother. How wrong I was!
The problem seems to be that when creating a new system when you get to the part where the speaker gets connected to the Wi-Fi network the app tells it to connect to the Wi-Fi network of the existing system, not the one you’re connected to and are trying to set it up on. This happened to me on both Android and iOS and using the same account as my home system and with a new account I setup fresh.
I finally found a way round it by using a spare device that had a fresh install of Sonos that hadn’t connected to any other Sonos system before. But that took a while as the first two device I tried were too old and the OS wasn’t supported (iOS 12 and Android 7). So after two days of trying I finally got there, but it would be good if the Sonos app was fixed to tell the new speaker to connect to the correct Wi-Fi network rather than picking up the one from a different system!