smartsheet_create_webhook.rb

#!/usr/bin/env ruby

require 'smartsheet'

webhook_url = "https://mattermost.example.com/hooks/yu6twumt93n89cjibmhdgz6mpa"
smartsheet_api_key = "<SMARTSHEET API KEY>"
smartsheet_id = "<SMARTSHEET ID>" # File > Properties on sheet

# Initialize the client - use your access token here
smartsheet_client = Smartsheet::Client.new(token: smartsheet_api_key)
# The `smartsheet_client` variable now contains access to all of the APIs

begin
  # This creates a webhook that fires when a column is updated
  mattermost_webhook = {
   name: "Mattermost",
   callbackUrl: webhook_url,
   scope: "sheet",
   scopeObjectId: smartsheet_id,
   events: ["*.*"],
   version: 1,
   subscope: {
    columnIds: [4912585878333316], # Be sure to replace this value
   }
  }

  hook = smartsheet_client.webhooks.create(body: mattermost_webhook)
  smartsheet_client.webhooks.update(webhook_id: hook['id'], body: {enabled: true})

rescue Smartsheet::ApiError => e
  puts "Error Code: #{e.error_code}"
  puts "Message: #{e.message}"
  puts "Ref Id: #{e.ref_id}"
end