Unfortunately Chromecast is currently not supported on the Nokia 3.
No chromecast? that is disappointing :(
Chromecast doesn't work well on most budget phones.
Actually, Chromecast is available for Nokia 3 because I do use it and it works pretty well. At least with me, it never failed.
You should uninstall/install it and see if works fine then. Or maybe it can be other software that is interfering with Chromecast.