# BT-21 — Invoice note subject code

> https://billhorse.com/en/terms/bt-21/

Qualifies what the free-text note (BT-22) is about (UNTDID 4451). UBL has no dedicated element — the code is embedded as a #CODE# prefix inside cbc:Note.

## Where does it live in the XML?

- UBL: `cbc:Note (Präfix #CODE#)`
- CII: `rsm:ExchangedDocument/ram:IncludedNote/ram:SubjectCode`