# BT-1 — Invoice number

> https://billhorse.com/en/terms/bt-1/

Unique identifier of the invoice, assigned by the seller. It identifies the document throughout the exchange and must not repeat per seller.

## Where does it live in the XML?

- UBL: `cbc:ID`
- CII: `rsm:ExchangedDocument/ram:ID`

## Checked by these rules

- [BR-02 — Invoice number missing](https://billhorse.com/en/rules/br-02/)