# File lib/active_merchant/billing/integrations/directebanking/helper.rb, line 65
          def generate_signature_string
            # format of signature: user_id|project_id|sender_holder|sender_account_number|sender_bank_code| sender_country_id|amount|currency_id|reason_1|reason_2|user_variable_0|user_variable_1|user_variable_2|user_variable_3|user_variable_4|user_variable_5|project_password
            SIGNATURE_FIELDS.map {|key| @fields[key.to_s]} * "|" + "|#{@project_password}"
          end