The part where your dialog, different than mine, says “Complete verification” means you have to perform those actions.
You must complete the verification process by placing a TXT record in a site’s DNS server.
Go into the website dropdown in your main builder profile under settings.
- Delete all the domains.
- Start the verification process again.
- Place the new token string into your DNS zone record.
- Wait 30 minutes or so for propagation.
- Press “Check” to confirm the new authentication token.
Then revisit your GPTs and make public.
I also would wait until there is a different email method than publishing your account’s details to users.