When your domain name is Newly Registered or has the DNS (Domain Name Servers) changed with your domain name registrar.

The changes are not instantly seen by Every ISP (Internet Service Provider).

Different ISP's around the world Can take up to 24-72 hours to update their DNS tables but most take only a few minutes so that everyone can see your website by entering your Domain Name.

You can check the progress of your DNS propagation by going to https://www.whatsmydns.net/