Hi @MikeToll welcome back to the forum. I had a search wound myself and can't find anything since it was added to the Cloud a few years back. Give the Cloud helpdesk a call on 0800 500 3114 (9am to 9pm Mon - Fri 9am to 6.30pm Sat and Sun) as they will be best placed to answer this for you.
I called the Cloud helpdesk as suggested and 1st Line had a chat with 2nd Line and concluded it wasn't a problem with BT Cloud and that I needed to pursue the issue with my phone provider. I explained that other apps were able to cast successfully from our three devices so you'd expect it to be the BT app that was having the issue. I was offered a callback by a 2nd-Line bod who did call back in the scheduled slot on 23/5 and took the details again and suggesting I'd get a call back, probably that evening... but disappointingly there hasn't been any follow up call.