code: def invoke_function(self, function_name, **function_params):
          
          url = self.build_url(self._endpoints.get('function').format(function_name))
          response = self.session.post(url, data=function_params)
          if not response:
              return None
          data = response.json()
  
          error = data.get('error')
          if error is None:
              return data.get('value')
          else:
              raise FunctionException(error)
docs: Invokes an Excel Function