A:Answer Unfortunately, T-Mobile app is not included on the list of cast-enabled apps. However, if you have an Android device, you can mirror your phone screen to the Chromecast to watch content from the T-Mobile app.
You may check the following support articles for more information:
Cast your Android screen: https://support.google.com/chromecast/answer/6059461
List of cast-enabled apps: https://store.google.com/us/product/chromecast_apps