# File lib/ruby-paypal/paypal.rb, line 216
      def do_express_checkout_payment(token, payment_action,payer_id, amount)
        params = {
          'METHOD' => 'DoExpressCheckoutPayment',
          'TOKEN' => token,
          'PAYMENTACTION' => payment_action,
          'PAYERID' => payer_id,
          'AMT' => amount
        }   
        make_nvp_call(params)    
      end