The external ID helps to identify the entity and a subsequent creation of an entity with the same ID will not create a new entity.
Invoice Merchant Reference
Last Completion
The last completion flag indicates if this is the last completion. After the last completion is created no further completions can be issued.
Line Items
The line items which will be used to complete the transaction.
Statement Descriptor
The statement descriptor that appears on a customer's bank statement, providing an explanation for charges or payments, helping customers identify the transaction.
Transaction ID
The ID of the transaction which should be completed.