This document provides a step-by-step guide on configuring and using Business Transaction Events (BTEs) in SAP FI to populate a custom value in an accounting document field. It describes BTEs and their differences from BADIs, the two types of BTE interfaces, and provides an example of using a process interface BTE to copy the text "Demo BTE" to the assignment field when a document is posted for a specific company code. The steps include identifying the BTE, creating and assigning a custom function module to the BTE, and testing the configuration.