I've tried to use multiple form plugins (Visual form builder, Ninja forms, form builder), and I have had the same problem with all plugins. Whenever I press the submit button, the page refreshes but nothing happens. However, when I do this in preview with all the plugins, it will save the entry in the database, and will show the "success message". So for whatever reason, the forms only submit in previews.
Link to current form: http://vinkhuiswerk.nl/aanmeldformulier/
Thanks in advance,