If you run into issues please be sure to try the following troubleshooting steps to resolve your issue:
Restart the app.
Reboot the Chromecast (How to Reboot)
Check your wifi connection. Make sure both your phone and Chromecast are connected to the same wifi network.
Check your network. If it is down, please contact your Internet Service Provider.
Display is powered on.
Display is on the right input.
Chromecast is powered on.
Chromecast has been setup properly. (How to Setup)
If you have more than 1 Chromecast, make sure you're casting to the correct Chromecast.
For additional Chromecast-related issues, please refer to the support page here.