アカウント有効化のメール送信送信メールのプレビューが開けない

前提・実現したいこと

Railsチュートリアル11章2.2 送信メールのプレビュー( https://railstutorial.jp/chapters/account_activation?version=5.1#sec-email_previews )で
アカウント有効化メールのプレビューが開けません。
発行されたURLに飛ぶとエラーが発生します。

発生している問題・エラーメッセージ

config/environments/development.rb
のhost名が違うと睨んでいるのでコードとその挙動を記載します。

Rails.application.configure do
  # Settings specified here will take precedence over those in config/application.rb.

  # In the development environment your application's code is reloaded on
  # every request. This slows down response time but is perfect for development
  # since you don't have to restart the web server when you make code changes.
  config.cache_classes = false

  # Do not eager load code on boot.
  config.eager_load = false

  # Show full error reports.
  config.consider_all_requests_local = true

  # Enable/disable caching. By default caching is disabled.
  if Rails.root.join('tmp/caching-dev.txt').exist?
    config.action_controller.perform_caching = true

    config.cache_store = :memory_store
    config.public_file_server.headers = {
      'Cache-Control' => "public, max-age=#{2.days.seconds.to_i}"
    }
  else
    config.action_controller.perform_caching = false

    config.cache_store = :null_store
  end

  # Don't care if the mailer can't send.
  config.action_mailer.raise_delivery_errors = true
  config.action_mailer.delivery_method = :test
  host = 'rails-tutorial-私のAWSアカウント名.c9users.io'
  config.action_mailer.default_url_options = { host: host, protocol: 'https' }

  
  config.action_mailer.perform_caching = false

  # Print deprecation notices to the Rails logger.
  config.active_support.deprecation = :log

  # Raise an error on page load if there are pending migrations.
  config.active_record.migration_error = :page_load

  # Debug mode disables concatenation and preprocessing of assets.
  # This option may cause significant delays in view rendering with a large
  # number of complex assets.
  config.assets.debug = true

  # Suppress logger output for asset requests.
  config.assets.quiet = true

  # Raises error for missing translations
  # config.action_view.raise_on_missing_translations = true

  # Use an evented file watcher to asynchronously detect changes in source code,
  # routes, locales, etc. This feature depends on the listen gem.
  config.file_watcher = ActiveSupport::EventedFileUpdateChecker
end

発行されたURLのメッセージ(host名を自分のAWSアカウント名にした場合)

No workspace is bound to this domain.

No Cloud9 workspace is bound to this domain name. Please check if the domain name is spelled correctly.

発行されたURLのメッセージ(host名を仮にmhartlにした場合)

Oops! We couldn't get you to 'rails-tutorial'

Cloud9 can't get you to your requested workspace. Here are some suggestions on how to figure out what's going on:

Check that the workspace name (rails-tutorial) and username (mhartl) are typed correctly.
Check that the server is successfully running on Cloud9:
If the server hit an error, the output window will have a message telling you what it is
If you're in the middle of debugging code, your server might be paused right now
The server might be running on a different port; make sure it's on port $PORT with $IP as the IP address