To get the Spark Room ID, go to web.ciscospark.com, select the room you want to post messages to and get the ID from the URL.

Example: https://web.ciscospark.com/#/rooms/f2fbc1f0-317c-11e6-8308-f3bee39e57c5
The Room ID would be: f2fbc1f0-317c-11e6-8308-f3bee39e57c5


You can also use the room ID representation acquired from GET https://api.ciscospark.com/v1/rooms

See https://developer.ciscospark.com/endpoint-rooms-get.html for more information