Sketch Mirror relies on your devices to be on the same network, and sometimes that’s not the case, giving you an error.
If you’re using a corporate / campus network, those are usually fire-walled, and the required traffic for Mirror is sometimes blocked by default. You may have to ask your network admin to add a rule to allow
_sketchmirror._tcp.local traffic in the network.
There is no official Android version of Sketch Mirror, but other people have built apps for Android that work well with Sketch: