Even if the phone can normally install apps not from the playstore, this apk in particular sometimes is blocked by any firewall or virus scanner you have on your phone. It didn't happen with the demo or our previous games really, so we're not entirely sure why it's happening now. But if you can check for anything on your phone that might scan files before they install, turning that off could help the download go through. Or maybe there's not enough space? The demo was a lot smaller. I'm happy you're excited for the game.