https://www.theverge.com/2017/11/14/16649586/sonos-pandora-premium-app-integration-controls

Starting today, you can control your Sonos speakers through Pandora’s mobile app. Users will be able to select rooms, group and ungroup speakers, and control the volume all from the Pandora app.

Spotify Connect allows users of the service to have similar control over their Sonos speakers, but you can’t group and ungroup speakers, and you have to pay for Premium to use any of its features; Pandora is letting all its users have access to its Sonos controls.