When you say “Sonys soundbar gen 1” do you mean the Sonos Playbar? If so, have you tried running TV Setup under the Playbar’s settings in the Sonos app?

Yes - when checking the connection it says no signal detected. 

Make sure the plastic caps on each end of the optical cable have been removed. Also make sure the optical cable has been fully inserted into the Playbar and TV.

Checked that. This is connected to the HDMI (eARC) on the tv and to the Sonos Optical adapter on the soundbar.  
 

shouldn’t I still see a red light at the end of the optical adapter? 

What specific Sonos sound bar do you own?

If you have a Sonos Playbar, you don’t need to use the optical adapter. You just need to use an optical cable from the Playbar to the optical port on the TV.

That is the way I started. Just can’t control the volume on the Sonos using the Roku remote (forces me to two remotes- Yuk).  
 

I have the original Sonos play-bar from 10 years ago. 
 

I went to the Sonos web site and there they suggested using the HDMI optical adapter to connect to the eARC connection - which does not work.