Connecting to a Sonos Soundbar

Can you please help with a problem I'm having. My satellite TV provider is DirecTV. I hooked up a Sonos Beam (GEN2) soundbar to an LG (smart) TV that receives its signal from a DirecTV receiver. The soundbar was hooked up to the LG TV using an HDMI cable plugging into the HDMI ARC input. There is no sound when the DirecTV signal is on (video perfect though no sound). When I turn on an app (e.g., YouTube, Netflix, etc.) the sound is perfect and I can control the volume with my LG controller.  Can you please tell me what I need to do to correct the audio problem. 

Thanks.