Need help getting 2 sensor values into 1

I have 2 sensors one for indoor and one for outdoor temp. Right now they are both listed as separate lines on my front end. I would like to make a new sensor that combines both of them into one reading like: Indoor Temp / Outdoor Temp with the space slash space between the 2.

I tried this:

# Indoor & Outdoor Temperatures
- alias: 'Indoor & Outdoor Temperatures'
  platform: template
  sensors:
    indoor_outdoor_temp:
      value_template: '{{ states.sensor.average_temp }} and {{ sensor.dark_sky_temperature }}'
      friendly_name: 'Indoor Outdoor Temp'

but it’s not working. Can anyone help me out with this line?:

 value_template: '{{ states.sensor.average_temp }} and {{ sensor.dark_sky_temperature }}'
 value_template: '{{ states.sensor.average_temp }} + " / " + {{ sensor.dark_sky_temperature }}'

Thanks!

value_template: '{{ states.sensor.average_temp.state }} / {{ states.sensor.dark_sky_temperature.state }}'

should do it.

Woo hoo! That worked. Thank you! I could have swore I tried that but apparently not. Much appreciated.