How to stop casting audio used in a flow?

Using the Google Chromecast app I have created a flow that plays music from TuneIn for my kids to get up. However, some mornings, they prefer to stop the music and the command, “Hey Google, stop” does not seem to do anything. Also tried “Stop casting” and that seems to not do anything either. It almost seems like nothing is playing when you look at the device in the GH app on the phone.

Hey google, stop casting on <castdevicename>
should work, regardless of the origin of the cast.