When I try to create a new Realm I get the error message "Realm name xxx is not allowed" with the default name or with something really simple.
I have seen the similar bug reports about problems renewing Realms and checked the account permissions as advised but it doesn't resolve the issue. I have selected 'allow' for absolutely everything on the account but still get the error. The account is a child account linked to my adult one.
I have tried logging in on iPhone, iPad and Android and got the same error on every device.
It sounds like you tried already, but have you specifically allowed the creating and joining of clubs?
If you are still having trouble please contact Mojang Customer Support directly, who should be able to help further.
Quick Links:
📓 Issue Guidelines – 💬 Community Support – 📧 Feedback – 📖 Game Wiki