I'm trying to change my permalink structure from default "http://www.graphicengine.ca/?p=123" to custom structure using "/%postname%/" and after setting it to this, WordPress automatically selects the Post name option "http://www.graphicengine.ca/sample-post/". Basically I want my page name to be shown in the URL.

When I test it out and click on my About Us page (http://www.graphicengine.ca/about-us/), I get 404 Not Found. When I go to my About Us page, it shows permalink: Permalink: http://www.graphicengine.ca/about-us/.

Not sure how to fix or if need to do something to .htaccess. Of course if I revert back to original permalink default, links work. Also, just to note I'm using Yoast SEO.

Any ideas how to fix?