Phoenix custom error doesn't work

I have read phoenix documents and edited my code but it didn’t work for me.

my dev config :

config :trangell_html_site_web, TrangellHtmlSiteWeb.Endpoint,
  http: [port: 9991],
  debug_errors: false,
  code_reloader: true,
  check_origin: false,
  watchers: [node: ["node_modules/brunch/bin/brunch", "watch", "--stdin",
                    cd: Path.expand("../assets", __DIR__)]]

my ErrorView :

  def render("404.html", _assigns) do
   "Page not found"
  end

  def render("500.html", _assigns) do
    "Server internal error"
  end

  def template_not_found(template, _assigns) do
    Phoenix.Controller.status_message_from_template(template)
  end

but it shows me :

55%20pm1440×900 123 KB

How can I fix this ?

ref

https://hexdocs.pm/phoenix/errors.html
https://hexdocs.pm/phoenix/views.html#the-errorview

phoenix 1.3 || elixir v1.6.4