code: def reference_id(self, reference_id):
          
  
          if reference_id is None:
              raise ValueError("Invalid value for `reference_id`, must not be `None`")
          if len(reference_id) > 40:
              raise ValueError("Invalid value for `reference_id`, length must be less than `40`")
  
          self._reference_id = reference_id
docs: Sets the reference_id of this Order.
          A client specified identifier to associate an entity in another system with this order.
  
          :param reference_id: The reference_id of this Order.
          :type: str