Do you have Anynet+ (CEC) turned on in your TV settings?

I dont believe I do no? I have not seen that option available in the settings either i’m afraid. 

Appreciate any further thoughts you may have though.

Is it under Settings > System > Expert Settings?

It feels as though there is no signal being sent between the two devices to recognise they are connected?

Is it under the wrench icon?

Found it and it appears to be “on” and would have always been? 

Keep Anynet+ set to On. Unplug your TV and Arc from power for about a minute and disconnect the Arc from the TV. Plug the TV back in and run TV Setup in the Sonos app. Connect the Arc to your TV’s HDMI eARC port when the app instructs you to.

Also check this setting:

Settings > Sound > Sound Output > select Receiver (HDMI)

Which HDMI port is the Arc connected to? Are you sure it’s the ARC or eARC port? 

And did you make sure the Sound Output setting is set to Receiver (HDMI)?

The system came with an optical adaptor for the HDMI. Is this an option we should look at?

No, this option is a last resort.

Can you try using the HDMI cable that came with the Arc?

I didn’t get one with it unfortunately 

That’s weird. Did you purchase it used? Do you have any other HDMI cables you can use?

OMG!!!! Thank you so much!! The issue was the cable! 
 

I feel a bit stupid on that back of all of that but I honestly can’t thank you enough for persevering with me! LEGEND!!!

Glad it was just the cable and not the Arc or your TV that was defective.

Be sure to set Sound Output to Receiver (HDMI), turn on Dolby Atmos Compatibility, and set Digital Output Audio Delay to 0.

Enjoy!