@Xrkt77 I called there but missed you, I've made arrangements for you to be changed over to the full version of the BT sport app as you were on the BT mobile version. The change over will complete in the next 24 hours and you'll be able to cast from the app.
Please can you post back to let me know if you're happy this is sorted?
I’m also a BT Infinity Broadband subscriber & have BT mobile. Can you arrange for me to be changed over to the full version of the BT Sport App as I think i’m on the BT mobile version, so that I can stream BT Sport onto my Apple TV.