anchor.diff:  * The invoice is a migration invoice (imported from a different billing system into Kill Bill)
   * The invoice corresponds to a child account and has a zero parent invoice balance
   
  +
   Let us now understand how the `charged amount` and `invoice balance` are computed in various scenarios.
   
   == Recurring Subscription
  
positive.code: ----
                  
  [start=2]
  . Next, when a https://killbill.github.io/slate/#credit-create-credits[credit is added] to the invoice (say `$20`), the invoice is modified.  A new invoice item is added of type `CREDIT_ADJ` and amount `-20`.
  
  So, `CHARGED AMOUNT` and `BALANCE` are calculated as follows:
  
  
negative.code: 
  Before we look at each scenario, let us understand how `charged amount` and `balance` are calculated. 
  
  
  [NOTE]
  *Note:* An invoice consists of one or more invoice items. Each invoice item is of a different type and its amount is either positive, negative or zero depending on the type. The invoice item `type` and `amount` heavily influence the `charged amount` and `balance` calculations explained in this document. It is therefore advisable to familiarize with invoice item type/amount by reading the https://docs.killbill.io/latest/userguide_subscription.html#components-invoicing-overview[subscription billing] document before proceeding further.
  
  === Charged Amount
  
  The `charged amount` (also known as `invoice amount`, `invoice total` or simply `amount`) specifies the amount that the customer is charged as part of an invoice. It is computed by adding up the amounts on invoice items of type `FIXED`, `RECURRING`, `EXTERNAL_CHARGE`, `USAGE`, `TAX`, `ITEM_ADJ`, `REPAIR_ADJ`, `PARENT_SUMMARY` and `CREDIT_ADJ`. Note that `PARENT_SUMMARY` invoice items are only applicable in the case of https://docs.killbill.io/latest/ha.html[hierarchical accounts] and will be skipped in the rest of this document.
  
  