Since 3.5.0 users can create new taxonomy terms from front-end forms created with Frontend Publishing Pro. Here are the settings that you need to change in order to use this functionality:

– In your admin panel, go to Frontend Publishing Pro > Forms and start editing the form that you want to enable this feature for.
– In the “Fields” tab, expand any taxonomy field e.g. Category.
– Select “Advanced Select” as the element type.
– Check the box titled “Allow addition of new items”.

That’s all. Now your users will not only be able to search through existing categories but will also be able to add new ones if no results are returned.