The Chromecast option is available on the iOS app where:
- You are on the same network as your Chromecast device,
- You are using iOS15 or later,
- You have given permission for the STV app to access that network.
You will need to give permission to individual apps to access your local network to connect to other devices - such as Chromecast. It's only required the first time after you update your device.
You will get a pop-up asking you to allow access to the network when you first log on to the app - click OK to allow access, and you can cast as normal.
You can change this setting at any time by going to Settings -> STV Player -> Local Network and toggling this to on/off - then Close and Restart to apply the new settings.
The cast icon should then be shown on the top right - next to the Search icon before playback, during playback it will be in the bottom right of the playback bar.