Why casting isn't available from iPhone and iPad browsers, and how to play on a TV today.
Browsers on iOS (Safari, Chrome, Firefox) don't support casting to Chromecast, so the "Send to TV" button can't connect to a Chromecast from the web app on an iPhone or iPad.
Direct AirPlay from the web app isn't supported yet — the native iOS app (in development) will add proper AirPlay support.