```ruby
# frozen_string_literal: true

class Pubsubhubbub::DeliveryWorker
  include Sidekiq::Worker
  include RoutingHelper

  sidekiq_options queue: 'push', retry: 3, dead: false

  sidekiq_retry_in do |count|
    5 * (count + 1)
  end

  def perform(subscription_id, payload)
    subscription = Subscription.find(subscription_id)
    headers      = {}

    headers['User-Agent']      = 'Mastodon/PubSubHubbub'
    headers['Link']            = LinkHeader.new([[api_push_url, [%w(rel hub)]], [account_url(subscription.account, format: :atom), [%w(rel self)]]]).to_s
    headers['X-Hub-Signature'] = signature(subscription.secret, payload) unless subscription.secret.blank?

    response = HTTP.timeout(:per_operation, write: 50, connect: 20, read: 50)
                   .headers(headers)
                   .post(subscription.callback_url, body: payload)

    raise "Delivery failed for #{subscription.callback_url}: HTTP #{response.code}" unless response.code > 199 && response.code < 300

    subscription.touch(:last_successful_delivery_at)
  end

  private

  def signature(secret, payload)
    hmac = OpenSSL::HMAC.hexdigest(OpenSSL::Digest.new('sha1'), secret, payload)
    "sha1=#{hmac}"
  end
end
```

Remove PuSH subscriptions when delivery is answered with a 4xx error
user
```ruby
# frozen_string_literal: true

class Pubsubhubbub::DeliveryWorker
  include Sidekiq::Worker
  include RoutingHelper

  sidekiq_options queue: 'push', retry: 3, dead: false

  sidekiq_retry_in do |count|
    5 * (count + 1)
  end

  def perform(subscription_id, payload)
    subscription = Subscription.find(subscription_id)
    headers      = {}

    headers['User-Agent']      = 'Mastodon/PubSubHubbub'
    headers['Link']            = LinkHeader.new([[api_push_url, [%w(rel hub)]], [account_url(subscription.account, format: :atom), [%w(rel self)]]]).to_s
    headers['X-Hub-Signature'] = signature(subscription.secret, payload) unless subscription.secret.blank?

    response = HTTP.timeout(:per_operation, write: 50, connect: 20, read: 50)
                   .headers(headers)
                   .post(subscription.callback_url, body: payload)

    return subscription.destroy! if response.code > 299 && response.code < 500 && response.code != 429 # HTTP 4xx means error is not temporary, except for 429 (throttling)
    raise "Delivery failed for #{subscription.callback_url}: HTTP #{response.code}" unless response.code > 199 && response.code < 300

    subscription.touch(:last_successful_delivery_at)
  end

  private

  def signature(secret, payload)
    hmac = OpenSSL::HMAC.hexdigest(OpenSSL::Digest.new('sha1'), secret, payload)
    "sha1=#{hmac}"
  end
end
```
assistant