Have you followed the steps in this article and run TV Setup under the Playbase settings in the Sonos app? Also make sure the caps have been removed from the optical cable and the cable has been fully inserted into the optical ports.

https://support.sonos.com/s/article/4780?language=en_US

Yes, I have tried going through the set up steps several times. 

Did you make sure the caps were removed from both ends of the cable as suggested by @GuitarSuperstar?

Also, try this…

Unplug all Sonos

Reset the Playbase

Unplug any range extenders and/or access points 

Reboot your router and let it come back

Delete the Sonos app

Update your device 

Install the Sonos app

Setup the Playbase

Add sub and surround if applicable

Plug in other Sonos 1x1 and let each come back before moving to next

Plug in extenders and/or access points; if needed. *

* If Sonos is setup properly but still encounters connection issues consider wiring either a Sonos Boost module or Sonos speaker (not a speaker used as a surround or sub) to your main router to create the SonosNet. Doing places Sonos on its own network bypassing your home WiFi.