The cable  needs to be hdmi 2.1 complaint for ARC/eARC.  This is pretty common if your buying new cables.  If you’re hoping to use an existing cable that’s not clearly marked, you can always give it a try before routing it through a wall.

Hi @Tj1057 

Welcome to the Sonos Community!

I hate to argue @melvimbe, but HDMI 2.1 is only needed for 4k@120Hz content (or 8k@60Hz). As we are only interested in getting audio to an Arc, a HDMI v2.0 cable will suffice for eARC - this should save a few pennies as compared to a 2.1 cable,

I hope this helps.

I will remember this offense forever.

Hi @melvimbe 

Thanks, what lengths can those be purchased in?

Hi @Tj1057 

For eARC, we don’t recommend going over 5 metres (15 feet). I imagine you can probably find 0.5m, 1m, 1.5m, 3m and 5m lengths without too much trouble.

I hope this helps.

Pretty much whatever size you need.  Just go to Amazon or your favorite store and you will see plenty of options.  Longer cables over 20 feet may need to be connected a specific way.  Even longer may require a booster for the signal.  I have used 20 ft + cables for Arc audio without issue.