Please allow up to 72 hours for the DNS name server update to fully propagate across the Internet.
Recursive DNS servers, like the one you query locally at your ISP cache the name servers responsible for your domain depending on the particular TLD (top level domain) your domain is under. Some update rather quickly like .com/net, while others may take a little longer. Also if your domain is cached locally on a recursive server, some name server operators opt to use higher TTLs (time to live) to reduce network traffic and load on their servers. Which could delay the amount of time it takes for your domain to start resolving on our name servers.
If after 72 hours, your domain still isn’t working, please contact No-IP’s support department.