code: def handle_error(self, exp):
          
          payload = {
              "message": "Invalid or incomplete data provided.",
              "errors": exp.errors
          }
          self.endpoint.return_error(self.error_status, payload=payload)
docs: Called if a Mapper returns MappingInvalid. Should handle the error
          and return it in the appropriate format, can be overridden in order
          to change the error format.
  
          :param exp: MappingInvalid exception raised