Check the audio settings on your TV. Set the Audio Out setting to the proper setting. Set TV Speakers Off and set the Digital Out Format setting to Multichannel. Do NOT choose the Multichannel (bypass) setting.

Thanks for your reply. I have tried the settings, but I still can't get any signal out of the TV. 

Try the Stereo (uncompressed) setting instead of Multichannel. Also be sure TV Autoplay is enabled under the Playbar’s settings in the Sonos app. And make sure the plastics caps have been removed from either end of the optical cable. Disconnect and reconnect the optical cable and listen for the click on each end.

Are you using any external media devices?

What source are you playing? The docs for this TV state:

SPDIF output (DIGITAL AUDIO OUT) will be disabled when streaming Dolby Digital Plus content

You might also need to adjust the SPDIF volume itself via Settings > Sound > Advanced > Digital out
levelling

Thanks for your support. I have tried every possible setting and nothing worked. Seems like there is a problem with the TV digital out. Today I have buyed an hdmi arc/toslink converter and connected it to hdmi on tv and optical in on my playbar. It worked immediately. After almost two years of waiting it's nice to have the SONOS sound back. :-)