I just bought Stadia with a Chromecast and I can't use it, always is stuck on "Checking your connection..." And I try in every game on the Stadia Pro and nothing, I don't know what I can do.
@Alejandcolina Might be an issue with your internet connection. Are you on WiFi or ethernet cable? If you're on WiFi, try if you can set the network to be 5Ghz, as I've seen some people having luck with it.
Otherwise, can you try launching a game from Chrome browser on a computer, or Stadia app on supported phone (if you have any)?
Also, which location are you trying to launch Stadia from?