According to Headspace, they’re not on the Sonos platform at this point. If you have an iPhone, and a Sonos speaker that can receive AirPlay 2, you could send the signal to your Sonos. Or, you could petition with Headspace to add themselves to the Sonos environment by pointing them to Sonos partners page. Sonos can’t add them willy nilly , it has to be done by the other company.