Example of ActiveMerchant Express Checkout request construction

payments_controller.rb

    amount = thing.build_payment.price_in_cents
    response = EXPRESS_GATEWAY.setup_authorization(amount,
      :ip                => request.remote_ip,
      :return_url        => new_payment_url,
      :cancel_return_url => new_order_url,
      :no_shipping        => true,
      :items             => [{:name => "#{thing.title}", :amount => amount}]
    )