A few things to maybe check in the LG TV sound Settings…

• Have you set the sound out in the TV settings to use Optical?
• Is the DTV setting set to Dolby Digital?
• Is the HDMI format set to Bitstream?
• Have you set the Digital Sound Out to either Auto, or Pass-through (if available)?

A few things to check on the Playbar/Cable…

• Check the optical cable is seated correctly with no plastic covers on ends of the cable.
• That the Playbar volume is not muted or so low that you cannot hear it
• With the Playbar Room in ‘focus’ and showing on the ‘now playing’ screen in the App, select the TV icon (below the list of Music Services) on the ‘Browse Tab’ to ensure TV audio is selected. If selecting this icon does makes the audio work, then goto ‘Settings/System/oPlaybar Room Name]’ and toggle ‘OFF’ then ‘ON’ the TV Autoplay feature and leave it ‘ON’. I would also recommend using the “Ungroup on Autoplay’ option too.

Is the Playbar listed in your system in the Sonos app? Have you redone the TV Setup process in the app?