As far as I’m aware, none of the Sonos products support the Amazon Alexa ‘Drop In’ service. It appears it’s exclusive to Amazon echo products only.

Thanks for the response Ken.  Arc isn’t listed as an incompatible product on other threads, that was the reason I thought it may have worked

I read on another thread that Drop In and messaging etc is possible on non-Amazon/Echo devices, but that they have to have some sort of visual sign or signal too. Ie an LED or flashing light like echo devices have. And since Sonos doesn’t have this they can’t have drop in. Whether that’s the ACTUAL reason it’s not enable I don’t know. But it looks like that is a restriction from Amazon.