I am also struggling with casting. I can connect my phone to my headset via my iOS mobile and settings. I am able to get the 5 digit pair pin from the settings --> about (rather unintuitive but found a reddit post).
But when I try to cast from the settings bar after clicking camera it doesn't recognize that I have paired. The iOS app doesn't seem to recognize that it is already paired.
It's a relatively frustrating experience and despite working in IT, I can't get it to work. I wonder how frustrating this is for non-technical users.
What is needed in order for me to get this to work? I'm happy to provide some screenshots if need be. It really feels like there's some software issues with the iOS mobile app.