When accessing a post type or taxonomy archive pages you might run into a 404 error, especially after changing the slug in the settings.
To fix, try going to the Settings > Permalinks page (this is the WordPress settings section, not the plugin settings). You’ll see something like this there:
To flush the permalinks, the only thing you have to do is click the blue “Save Changes” button at the bottom. So no need to actually change any settings, just clicking on the button.
Saving those changes basically forces WordPress to regenerate all the rewrite rules needed to make all permalinks work. This can fix 404 errors in some cases (for example if you recently changed settings).