If the browser says that your website cannot be reached because the server IP address could not be found, you should check the domain settings on the registrar's website (where you bought the domain name). Read this guide to find out how.
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If the browser says that your connection is not private, you are probably trying to open your website using the HTTPS protocol without properly configuring it. Replace "https" with "http" in the address bar or configure HTTPS on your website.