    # File lib/active_merchant/billing/gateways/authorize_net.rb, line 150
          def credit(money, identification, options = {})
            requires!(options, :card_number)

            post = { :trans_id => identification,
                     :card_num => options[:card_number]
                   }
            add_invoice(post, options)

            commit('CREDIT', money, post)
          end