I don't understand what I should do to set up my builder profile

I created an gpt and i want to publish it, but i need to set up my profile first.
I’m going here and i don’t know what to do next. What kind of domain does it need? Can someone tell me step by step what to do?

As I tried, any domain is ok, a.com or b.a.com. Just followed the instruction.
But there is a bug in selecting domains if you have multiple domains.

ok, great, where can I find instruction?

click “add domain” button, it will show the DNS txt record you need to set.