Setting up Nest Thermostat to Eco in a Scene

Configuration
1

Hi,

I am trying to put my Nest Thermostat to Eco mode using a scene.

scene:
  - name: Sleep
    entities:
       climate.downstairs:
           preset_mode: eco

This is throwing an error:

Logger: homeassistant.config
Source: config.py:854
First occurred: 10:44:24 AM (4 occurrences)
Last logged: 12:26:26 PM

Invalid config for [scene]: State for climate.downstairs should be a string for dictionary value @ data[‘states’][0][‘entities’]. Got None. (See /config/configuration.yaml, line 263). Please check the docs at Scenes - Home Assistant

What am I doing wrong?

TIA