I am trying to cast from Android app to Apple TV 3rd Gen but when I click the cast button I do not see my appletv. I can see the appletv from my wife's macbook perfectly fine so I am wondering is this is an Android app issue?
ATV3 has no casting support besides airplay. iDevices have airplay embedded, so they can see ATV3's (with or without Plex). Not the case of Android devices, where you need to install airplay support via a separate app.
Have you ever considered PlexConnect instead ? It does not supports casting either, but is able to stream your Plex library to your TV and/or amplifier.
It was a network issue. It is working now. Thanks