code: def setExpressCheckout(self, params):
          
          if self._is_recurring(params):
              params = self._recurring_setExpressCheckout_adapter(params)
  
          defaults = {"method": "SetExpressCheckout", "noshipping": 1}
          required = ["returnurl", "cancelurl", "paymentrequest_0_amt"]
          nvp_obj = self._fetch(params, required, defaults)
          if nvp_obj.flag:
              raise PayPalFailure(nvp_obj.flag_info, nvp=nvp_obj)
          return nvp_obj
docs: Initiates an Express Checkout transaction.
          Optionally, the SetExpressCheckout API operation can set up billing agreements for
          reference transactions and recurring payments.
          Returns a NVP instance - check for token and payerid to continue!