PayPal Integration

Hi i was following this link
http://www.funonrails.com/search?q=paypal&imageField.x=0&imageField.y=0&max-results=10
for PayPal integration in the process i got this error

undefined local variable or method `pay_bill_url' for
#<#<Class:0x927b3f8>:0x92794b8>

View Name:create
<%= form_for @payment ||= Payment.new, :url => pay_bill_url, :html => {:id
=> :payForm} do |p| %>
<%=p.text_field :amount%>
<%=p.submit 'Pay'%>
<% end %>

Controller Name: billing

class BillingController < ApplicationController
  before_filter :get_order, :only => [:checkout, :paypal, :thank_you]

def new
    @payment = Payment.new params[:payment]
    if @payment.save
      ## Paypal Checkout page
      redirect_to billing_url
    else
      render :action => :new
    end
end

  def create

  end

  # ASSUMPTION
  # order is valid i.e. amount is entered

  def checkout
    response = @order.setup_purchase(:return_url =>
confirm_paypal_url(@order), :cancel_return_url => root_url)
    redirect_to @order.redirect_url_for(response.token)
  end

  ## CALL BACK
   def paypal
     @order = @order.purchase(:token => params[:token], :payer_id =>
params[:PayerID], :ip => request.remote_ip)
     @order.save redirect_to thank_you_billing_url(@order)
   end

   private
   def get_order
     @order = Payment.find_by_id(params[:id])
     @order && @order.valid? || invalid_url
   end

end

Routes:
match 'billing/create' => 'billing#create'
## Callback URL
match '/billing/paypal/:id/confirm', :to => 'billing#paypal', :as =>
:confirm_paypal
## Create payment
  #match '/billing', :to => 'billing#create', :as => :pay_bill

Is this the line that should give you pay_bill_url? If you look
closely you will see it is not quite correct. If you cannot see it
examine every character on the line and work out what that character
does.

Colin