Rails3 ActiveMerchant Paypal Express Checkout Money Transfer - ruby-on-rails-3

Question

I am trying to implement PaypalExpressCheckout in my e-commerce application which is built on Rails3.
There will be two roles in the application - Seller and Buyer
Seller can create products and he can add his valid Paypal Email address to get amount on behalf of his sold products.
Buyer able to purchase items and can checkout through Paypal, amount shall transfer to the seller account once the user transaction is successful.
The issue I'm facing here, when buyer checking out, the amount is successfully transfer to the seller account but not deducting same from the buyer account.
I configured API credentials from Paypal sandbox and here are the methods I'm using from ActiveMerchant gem:
From Controller:
def checkout
values = {:ip => request.remote_ip,
:return_url => confirm_paypal_url(#payment),
:cancel_return_url => root_url, :shipping => 0,
:handling => 0, :tax => 0,
:items => get_items(session[:cart])}
response = #payment.setup_purchase(values)
redirect_to #payment.redirect_url_for(response.token)
end
## CALL BACK
def paypal
# session[:product_users] = [{:amount => '100', :email => 'xx#x.com'}]
session[:product_users].each do |user|
#payment = if user.last.nil?
#payment.purchase(:token => params[:token], :payer_id => params[:PayerID], :ip => request.remote_ip)
else
#payment.transfer(user[:amount], user[:email])
end
#payment.save
end
redirect_to billing_thank_you_url(#payment)
end
From Model:
def setup_purchase(options)
gateway.setup_purchase(amount * 100, options)
end
def transfer(amount, receiver)
response = gateway.transfer(amount * 100, receiver, :subject => "Payment from XXX")
end
I'd be grateful if anyone help me on this.
Thank You