BBC iplayer won’t cast on chromecast

I have BBC iplayer app on my iphone and I have vpn pointed to the UK, and the all the films and tv series play just well on the app but the problem starts when I tried to cast it. There’s the cast icon and my TV shows this screen from iplayer ”ready to cast” thing but whenever I click play, the window reverts back/close down to the previous. Any idea and solution to this? Thank you 🙏🏻