There are four types of transaction flexfields used by AutoInvoice:
Line Transaction Flexfield
Link-to Transaction Flexfield
Reference Transaction Flexfield
Invoice Transaction Flexfield
If you are using Autoinvoice, it is mandatory to define: (1) Line Transaction Flexfield (line level information) and (2) Invoice Transaction Flexfield (header level information). If you do not explicitly define Link-to and Reference Transaction flexfields, Autoinvoice will use the flexfield structure of the Line Transaction Flexfield to determine Link-To and Reference information.
This document discusses the various transaction flexfields and demonstrates how to setup each of the four types. The setup for Line Transaction Flexfield is discussed in most detail as it is required for the case study in Note 1067402.1, Setting Up AutoInvoice for Release 12: A Case Study using a Simple Script.