rails balanced troubleshooting

error.txt

undefined local variable or method `card_href' for #<PayController:0x00000105199190>

bombing on this line:
card = Balanced::Card.fetch(card_href)

pay_controller.rb

class PayController < ApplicationController
  require 'balanced'
  
  before_action :authorize_admin, only: [:paytest]

  def paytest
    Balanced.configure('ak-test-21bWfAC3dvIUE9uVhZu0u7IGMtVIOzkUV')

    card = Balanced::Card.new(
      :name => 'John Doe',
      :expiration_month => '12',
      :number => '5105105105105100',
      :expiration_year => '2020',
      :security_code => '123'
    ).save

    # card_href is the stored href for the Card
    card = Balanced::Card.fetch(card_href)
    card.debit(
      :amount => 10,
      :appears_on_statement_as => 'Statement text',
      :description => 'Some descriptive text for the debit in the dashboard'
    )

    @escrow = Balanced::Marketplace.mine.in_escrow
  end

  private

  def authorize_admin
    if !current_user.try(:admin?)
      redirect_to :controller => :'/home', :action => :index
    end
  end
end