My Registrar Says No-IP’s DNS Servers are Not Authoritative?

Some domain name registrars verify that DNS zone information is available on the new name server you are switching to before they will update the name server records.

If you have just recently activated your No-IP Plus or No-IP Squared domain, it can take up to 2 hours to become live on all of our DNS server nodes.

You should try processing the name server changes after this time period has passed to see if you still get a not authoritative notification. Some registrars including .de, .br, and .au registrars enforce this type of policy.