My pages or posts are showing a 404 Error Page Not Found
The most common cause of this issue are permalink settings in WordPress. To solve this issue you would need to reconfigure the permalinks settings or manually update your rewrite rules.
This usually happens if your .htaccess file got deleted or something went wrong with the rewrite rules. What you need to do is fix your permalinks settings.
Go to Settings » Permalinks, and simply click on Save Changes button.