Chromecast and the iOs app work best when recently re-synced to the same WiFi network.
First, please select the workout video you wish to stream select the CAST icon. Once you select the CAST icon you will need to select the Chromecast device you wish to connect to. Once connected your app screen will let you know by showing which device you are casting to. To disconnect, click the cast icon and then THIS DEVICE and LMOD will be displayed back on your app.