I was adding (3) Sonos One SL units to an existing system consisting of a Sonos Beam and (3) gen3 Play 1 units and ran into the exact same issue.  Pounding my head against a wall for HOURS, rebooting and resetting the new units and getting knee deep into my router, etc..and I can see everything in the table of connected devices…still nothing.  So, I unplugged every unit and one by one started resetting to factory default and voila!  Everything is good to go…and it only took about a ½ hr to get that done.  Wish I could get all that time back!