Blocked host error after deploying

Hi team!

After successfully deploying, I get this error which I don’t seem to be able to fix (probably due to lack of rails knowledge).
I tried to add
config.hosts << “
to the production.rb but still same error.

Would anyone be able to help please?

To allow requests to make sure it is a valid hostname (containing only numbers, letters, dashes and dots), then add the following to your environment configuration:
config.hosts << ""
For more details view: the Host Authorization guide
require "active_support/core_ext/integer/time"

# rubocop:disable Metrics/BlockLength
Rails.application.configure do
  # Allow the app to know when booted up in context where we haven't set ENV vars
  # If we have not set this ENV var it means we haven't set the environment
  ENV["ENV_AVAILABLE"] = ENV["APP_DOMAIN"].present?.to_s

  if ENV["ENV_AVAILABLE"] == "false"
    # We still need _something_ here, but if booted without environment (aka asset precompile),
    # it shouldn't need to be the proper value
  # Settings specified here will take precedence over those in config/application.rb.

  # Code is not reloaded between requests.
  config.cache_classes = true
  # Eager load code on boot. This eager loads most of Rails and
  # your application in memory, allowing both threaded web servers
  # and those relying on copy on write to perform better.
  # Rake tasks automatically ignore this option for performance.
  config.eager_load = true

  # Full error reports are disabled and caching is turned on.
  config.consider_all_requests_local       = false
  config.action_controller.perform_caching = true

  # Ensures that a master key has been made available in either ENV["RAILS_MASTER_KEY"]
  # or in config/master.key. This key is used to decrypt credentials (and other encrypted files).
  # config.require_master_key = true

  # Attempt to read encrypted secrets from `config/secrets.yml.enc`.
  # Requires an encryption key in `ENV["RAILS_MASTER_KEY"]` or
  # `config/secrets.yml.key`.
  config.read_encrypted_secrets = true

  # Disable serving static files from the `/public` folder by default since
  # Apache or NGINX already handles this.
  config.public_file_server.enabled = ENV["RAILS_SERVE_STATIC_FILES"].present?
  config.public_file_server.headers = {
    "Cache-Control" => "public, s-maxage=#{30.days.to_i}, max-age=#{3000.days.to_i}"

  # Compress JavaScripts and CSS.
  config.assets.js_compressor = :uglify_with_source_maps
  # config.assets.css_compressor = :sass

  # Do not fallback to assets pipeline if a precompiled asset is missed.
  config.assets.compile = true

  # `config.assets.precompile` and `config.assets.version` have moved to config/initializers/assets.rb
  config.assets.digest = true

  # Enable serving of images, stylesheets, and JavaScripts from an asset server.
  config.action_controller.asset_host = ENV.fetch("FASTLY_CDN_URL", nil)

  # Specifies the header that your server uses for sending files.
  # config.action_dispatch.x_sendfile_header = 'X-Sendfile' # for Apache
  # config.action_dispatch.x_sendfile_header = 'X-Accel-Redirect' # for NGINX

  # Force all access to the app over SSL, use Strict-Transport-Security, and use secure cookies.
  config.force_ssl = ENV["FORCE_SSL_IN_RAILS"] == "true"

  # Use the lowest log level to ensure availability of diagnostic information
  # when problems arise.
  config.log_level = ENV.fetch("LOG_LEVEL", :error)

  # Prepend all log lines with the following tags.
  config.log_tags = [:request_id]
  config.hosts << ""
  # Use a different cache store in production.
  # DEV uses the RedisCloud Heroku Add-On which comes with the predefined env variable REDISCLOUD_URL
  redis_url = ENV.fetch("REDISCLOUD_URL", nil)
  redis_url ||= ENV.fetch("REDIS_URL", nil)
  default_expiration = 24.hours.to_i
  config.cache_store = :redis_cache_store, { url: redis_url, expires_in: default_expiration }

  config.action_mailer.perform_caching = false

  # Ignore bad email addresses and do not raise email delivery errors.
  # Set this to true and configure the email server for immediate delivery to raise delivery errors.
  # config.action_mailer.raise_delivery_errors = false

  # Enable locale fallbacks for I18n (makes lookups for any locale fall back to
  # the I18n.default_locale when a translation cannot be found).
  config.i18n.fallbacks = true

  # Send deprecation notices to registered listeners.
  config.active_support.deprecation = :notify

  # Log disallowed deprecations.
  config.active_support.disallowed_deprecation = :log

  # Tell Active Support which deprecation messages to disallow.
  config.active_support.disallowed_deprecation_warnings = []

  # Filter sensitive information from production logs
  config.filter_parameters += %i[
    auth_data_dump content email encrypted
    encrypted_password message_html message_markdown
    password previous_refresh_token refresh_token secret
    to token current_sign_in_ip last_sign_in_ip
    reset_password_token remember_token unconfirmed_email

  # Use default logging formatter so that PID and timestamp are not suppressed.
  config.log_formatter =

  if ENV["RAILS_LOG_TO_STDOUT"].present?
    # Use a different logger for distributed setups.
    # require 'syslog/logger'
    # config.logger = 'app-name')

    logger           =$stdout)
    logger.formatter = config.log_formatter
    config.logger    =

  # Do not dump schema after migrations.
  config.active_record.dump_schema_after_migration = false

  protocol = ENV.fetch("APP_PROTOCOL", "http://")

  config.action_mailer.delivery_method = :smtp
  config.action_mailer.perform_deliveries = false
  config.action_mailer.default_url_options = { host: protocol + ENV["APP_DOMAIN"].to_s }

    config.middleware.use Rack::HostRedirect,
                          ENV.fetch("HEROKU_APP_URL", nil) => ENV.fetch("APP_DOMAIN", nil)

  # Inserts middleware to perform automatic connection switching.
  # The `database_selector` hash is used to pass options to the DatabaseSelector
  # middleware. The `delay` is used to determine how long to wait after a write
  # to send a subsequent read to the primary.
  # The `database_resolver` class is used by the middleware to determine which
  # database is appropriate to use based on the time delay.
  # The `database_resolver_context` class is used by the middleware to set
  # timestamps for the last write to the primary. The resolver uses the context
  # class timestamps to determine how long to wait before reading from the
  # replica.
  # By default Rails will store a last write timestamp in the session. The
  # DatabaseSelector middleware is designed as such you can define your own
  # strategy for connection switching and pass that into the middleware through
  # these configuration options.
  # config.active_record.database_selector = { delay: 2.seconds }
  # config.active_record.database_resolver = ActiveRecord::Middleware::DatabaseSelector::Resolver
  # config.active_record.database_resolver_context = ActiveRecord::Middleware::DatabaseSelector::Resolver::Session
# rubocop:enable Metrics/BlockLength

Rails.application.routes.default_url_options = {
  protocol: ENV.fetch("APP_PROTOCOL", "http://").delete_suffix("://")

@knhchris ,
were you able resolve the above issue ?
what version of Rails are you using ?
check this article [Ruby On Rails | Blocked Host: localhost - Stack Overflow](blocked host error after deploying)