anchor.diff:  |SUBSCRIPTION_CANCEL
   |Occurs when a subscription is cancelled
   |SUBSCRIPTION_UNCANCEL
  -|Occurs when a subscription cancellation is undone (Note that subscription cancellation  cannot be undone once the cancellation becomes effective)
  +|Occurs when a subscription cancellation is undone (Note that subscription cancellation cannot be undone once the cancellation becomes effective)
   |SUBSCRIPTION_BCD_CHANGE
   |Occurs when the subscription billing date is changed
   |ENTITLEMENT_CREATION
  
positive.code: 
  When the `NotificationPluginApiRetryException` is caught by Kill Bill, the system computes the next retry date based on the schedule specified in the exception and the number of times that specific event has been retried. 
  
  So, in terms of responsabilities:
  
  * Plugin is in charge of deciding whether a `NotificationPluginApiRetryException` should be thrown and attach the associated retry schedule to it.
  * Kill Bill manages the retry logic and also keeps count of # existing retries versus retry schedule.
  
negative.code: |ACCOUNT_CHANGE
  |Occurs when a customer account is modified
  |BLOCKING_STATE
  |Occurs when there is a change in the state of an entitlement or billing. See https://killbill.github.io/slate/#account-blocking-state[Blocking States] to know more
  |BROADCAST_SERVICE
  |Used to broadcast an event to other Kill Bill nodes (Typically used for plugin related events like plugin installation, plugin uninstallation, plugin start, plugin stop, etc.)
  |SUBSCRIPTION_CREATION
  |Occurs when a new subscription is created
  |SUBSCRIPTION_PHASE
  