Hi @thenns. Thanks for being part of GoDaddy Community! It sounds like you've already registered the domain hosts so you can use custom nameservers. If you're still seeing that error, I'd recommend double-checking to make sure the nameserver hosts appear as registered externally. You can do so by using a DNS check, like this one. If the hosts are registered and you're still seeing the error, then I'd suggest getting in touch with our customer care team so they can take a closer look.
JesseW - GoDaddy | Community Manager | 24/7 support available at x.co/247support | Remember to choose a solution and give kudos.