Not clear how to make preview work

[nleo]

I use html, so I add

Markitup::Rails.configure do |config|
  config.formatter = -> markup { simple_format markup }
end

mount Markitup::Rails::Engine, at: "markitup", as: "markitup"

And get error 404 http://localhost:3000/projects/62/posts/25/templates/preview.html

But from placed by url http://localhost:3000/projects/62-bru/posts/25/comments

Why it not try to render preview somthing like http://localhost:3000/markitup/preveiw?text=...