I observe some strange behavior of form_for helper in my template. Could somebody help me?

#error:
== Compilation error in file lib/webtestapp_web/views/payment_view.ex ==
** (CompileError) lib/webtestapp_web/templates/payment/index.html.eex:1: undefined function payment_path/2
...

#mix phx.routes
page_path  GET   /              WebtestappWeb.PageController :index
payment_path  GET   /payments/new  WebtestappWeb.PaymentController :new
payment_path  POST  /payments      WebtestappWeb.PaymentController :create

# index.html.eex
...
<%= form_for @conn, payment_path(@conn, :create), [as: :params], fn f -> %>
...

# router.ex
...
resources "/payments", PaymentController, only: [:new, :create]
...

#payment_controller.ex
defmodule WebtestappWeb.PaymentController do
  use WebtestappWeb, :controller

  def new(conn, _params) do
    render(conn, "index.html", conn: conn)
  end
...

# payment_view.ex
defmodule WebtestappWeb.PaymentView do
  use WebtestappWeb, :view
end