Flush rewrite rules

Whenever a new custom post is added (such as ‘Portfolio’ in our case) through a plugin or code, WordPress permalinks usually need to be flushed.

Flushing rewrite rules is also necessary when you encounter an ‘Error 404’ on pages you know exist.

Navigate to your site admin area -> Settings -> Permalinks, then click the ‘Save Changes’ button. This action will refresh the permalinks cache.