WordPress doesn’t have an obvious way to include sub categories in the permalink structure. Sure, categories are easy enough to include. You just set up permalinks in the settings to include the /%category%/ variable and tick the desired category in your post and it shows up in your address bar.
The issue comes along when you want your permalink structure to look something like:
To achieve the above, all you have to do is not tick your parent category when saving your post, but rather tick the sub category only. There you, just a simple tip, but it caught me off guard last week, and it might catch you too.