My streamer doesn't appear in the output list

Serento drives streamers over UPnP AV or OpenHome. A device that only speaks AirPlay, Chromecast, Spotify Connect or a manufacturer's own protocol cannot be controlled, no matter how good it sounds. Sonos, in particular, does not expose a usable UPnP renderer.

If your streamer does support UPnP and still does not appear:

• Same network segment. Many routers isolate wireless clients from wired ones, or put guest Wi-Fi on its own segment. Discovery uses multicast, which does not cross those boundaries.
• The streamer has to be awake. Some devices stop advertising in standby.
• Wi-Fi extenders and mesh systems often drop multicast between nodes. If the streamer appears when your phone is next to the main router but not elsewhere, that is the cause.

Serento re-scans periodically and when you bring it back to the foreground, so a device that wakes up later will appear without you doing anything.