I did all the instructions correctly but screen Mirroring just doesn't work. I made sure screen Mirroring option is on "Always allow." But when I get to my Android phone, Roku 3 doesn't show up when I click cast. I'm using a Moto g6, so I'm not sure if that has to do with it.
Not all Android phones will cast to non-Chromecast devices, especially if, like Moto phones, have stock or near-stock Android. I have a G5+, and it also will not see any cast device (Roku or even myBD player.)
I have a moto e5 plus and after messing with it, found that its default Cast function works only with Chromecast devices. But you can download mirroring apps that will talk to Roku and other devices. My problem is that I can only get it to mirror videos that i have stored on my phone. I thought the whole idea of mirroring was to have it cast whatever is on my phone's display?
Think of it this way..... CAST = cast a stored video or photos using an app on the phone like a media player to cast or throw the playback to an app on the TV that can take over the playback. Such as youtube. You can turn your phone off after it's casted (thrown) to the cast device (miracast tv or chromecast) because the device receiving the cast is now doing the work. ........ MIRROR = mirroring/copying your phones screen to the TV screen. This is useful to show things on your phone that your TV can't cast receive. Like a browser or Google map. also you can't turn off your phone and it sucks your battery fast. This is like using your TV as a monitor only. Like hooking a monitor to your notebook computer the monitor is not doing any of the work , the phone/notebook is doing all the work ...... It's 2 distinctively different techniques with their own names.
Yeah it doesn't work and it's more than likely on purpose. They, as in Google and others, DO NOT want you to be able to do this. Why not make this possible instead of blocking it for your users? There is a large percentage of people that WILL NOT pay for services like Youtube tv etc.
However, you can still display media (photos, movies, music) from your MotoG (and other Google-like Android) phone to your Roku device using the "Play on Roku" feature in the Roku Mobile App (also works on iOS).
See the following Roku Support article for more detail on this: