I'm a free domain user because I'm a student and I don't have money to buy a domain name, I'm using jsdelivr.dev.tc domain name to build jsdelivr's mirror site, but when I add a domain name, it asks for _vercel.dev.tc domain name validation, but in fact, I only have the right to use the domain name of jsdelivr.dev.tc.Why do I need to verify the root domain instead of _vercel.jsdelivr.dev.tc?