pass refId in AuthorizeNet::ARB::Subscription.new()

I am using AuthorizeNet gem with recurring billing for subscription, I am able to get success response, code and subscription_id. But reference_id => nil

subscription = AuthorizeNet::ARB::Subscription.new(:refId => '1234546687567',
                                                   :name => "Master",
                                                   :length => 1,    
                                                   :unit => :month,
                                                   :start_date => Date.today,
                                                   :total_occurrences => :unlimited,
                                                   :amount => 799.00,
                                                   :invoice_number => '1234567',
                                                   :description => "John Doe's Monthly Gift Basket",
                                                   :credit_card => AuthorizeNet::CreditCard.new('4111111111111111', '1120'),
                                                   :billing_address => AuthorizeNet::Address.new(:first_name => 'test', :last_name => 'tester')
                                                  )

I want to pass refID in the function to get @reference_id value from success response. Please explain where I am doing wrong.