# BR-CL-08: Put an upper-case UNTDID 4451 subject code between the hashes of an invoice note

Three characters between the first two `#` of an invoice note are read as a subject code and must be on the UNTDID 4451 list, in upper case, as in `#AAI#`.

- Layer: EN 16931
- Severity: fatal (the document is invalid)
- Topics: Code lists, Core fields
- Official definition: https://docs.peppol.eu/poacc/billing/3.0/rules/ubl-tc434/BR-CL-08/
- Explanation last updated: 2026-09-28

## The short answer

`BR-CL-08` fails when an invoice-level `cbc:Note` has exactly three characters between its first and second `#`, and those three are not found in the UNTDID 4451 list. The recorded note began `#aai#`; the codes are upper case, so the corrected note begins `#AAI#`, General information.

In UBL the note subject code (`BT-21`) travels inside the note text in this `#CODE#` form. A note that is not meant to carry a subject code must not happen to contain three characters between two hashes either.

## What the rule checks

The rule reads each `cbc:Note` directly under the root and takes the text between its first two `#` characters. Only when that text is exactly three characters long is it looked up; otherwise the note passes. When tried, `#INFO#` with four letters and a note with a single `#` both passed.

The code does not have to open the note. When tried, `Please quote #XYZ# when you pay` failed, and so did `Order #123# delivered in full`, because `123` sits between two hashes.

Nothing is trimmed or folded to upper case. When tried, `#aai#` failed, and so did the invented `#INF#`. The lookup searches the list as one string of codes separated by spaces, so three characters that include a space can pass: `#A A#` did when tried.

Line notes are outside the rule. When tried, `#aai#` at the start of a line `cbc:Note` passed.

| Term | Meaning | UBL element |
|---|---|---|
| BT-21 | Invoice note subject code | `cbc:Note (the three characters between the first two # signs)` |
| BT-22 | Invoice note | `cbc:Note` |

## How an integration ends up here

Possible causes, from the shape of the rule rather than from measured usage:

- A template writes the subject code in lower case, as in the recorded example.
- The integration makes up a code from a word, such as `#INF#` for information or `#VAT#` for a tax remark, instead of taking one from the list.
- Free text typed by the seller contains a reference between hashes, such as an order number, with exactly three characters in the first pair.

## How to fix it

1. Decide whether the note needs a subject code at all; a note without one is valid.
2. If it does, take the code from UNTDID 4451 and write it in upper case between two hashes at the very start of the note, then the text: `#AAI#` for General information.
3. If free text can contain `#`, replace the character before writing the note, or put a real subject code first so that the first pair of hashes always holds it.
4. Offer the subject codes your system uses as a fixed choice, checked against the list, rather than letting users type them.

## Before and after

These are fragments, not complete documents. The complete synthetic documents they come from are linked below.

Fragment of the failing invoice: the note subject code is written in lower case

```xml
<cbc:InvoiceTypeCode>380</cbc:InvoiceTypeCode>
<cbc:Note>#aai#Please quote the invoice number when you pay</cbc:Note>
<cbc:DocumentCurrencyCode>GBP</cbc:DocumentCurrencyCode>
```

Fragment of the corrected invoice: the subject code is AAI, General information

```xml
<cbc:InvoiceTypeCode>380</cbc:InvoiceTypeCode>
<cbc:Note>#AAI#Please quote the invoice number when you pay</cbc:Note>
<cbc:DocumentCurrencyCode>GBP</cbc:DocumentCurrencyCode>
```

Only the case of the subject code differs: `#aai#` in the failing invoice, `#AAI#` in the corrected one, with the same text after it. The failing document reports `BR-CL-08` alone, and the Peppol layer passed.

### What the validator reported

- The failing invoice reports **BR-CL-08**. The corrected document passes every layer with no findings.
  - [Download the failing XML](https://ironfang.com/finance/rule-examples/BR-CL-08-invalid.xml)
  - [Download the corrected XML](https://ironfang.com/finance/rule-examples/codelist-note-subject-valid.xml)

Recorded on phive 12.1.0 / phive-rules-peppol 4.5.6 / Saxon-HE 12.10, the engine behind the free validator, using synthetic data. A recorded result is regression evidence for these documents; it is not a certification.

## Where it applies

- Applies to `Invoice` and `CreditNote`; `#aai#` at the start of a credit note `cbc:Note` reported this rule alone when tried.
- The Peppol layer does not look at subject codes, but it limits the number of notes: unless seller and buyer are both German, a second `cbc:Note` is reported by `PEPPOL-EN16931-R002`. When tried, two notes, the second beginning `#aai#`, reported both rules.
- The pinned list has 383 codes. Check a code against the list of this release rather than an older copy of UNTDID 4451.

## Related rules

- [PEPPOL-EN16931-R002 allows only one invoice note outside German domestic trade](https://ironfang.com/docs/finance/rules/PEPPOL-EN16931-R002.md)
- [PEPPOL-EN16931-CL003 rejects a note subject code such as DEL when it is reused as a charge reason code](https://ironfang.com/docs/finance/rules/PEPPOL-EN16931-CL003.md)

## Scope and source

Written for Peppol BIS Billing 3.0.21 (May 2026), EN 16931 1.3.16, as applied to UBL 2.1 Invoice and CreditNote documents. Other profiles, syntaxes and releases can define this identifier differently. Guidance version 2026-09-28.1: source checked 2026-09-28, explanation last updated 2026-09-28.

[The official definition of BR-CL-08](https://docs.peppol.eu/poacc/billing/3.0/rules/ubl-tc434/BR-CL-08/) carries the normative wording and test. This page is our explanation of it, not a copy.

Guidance does not change the engine verdict. Fixing this finding does not mean the document passes every layer, and validation does not certify legal or tax compliance or transmit a document over Peppol.

## Links

- [This rule as a web page](https://ironfang.com/docs/finance/rules/BR-CL-08)
- [Free Peppol invoice validator](https://ironfang.com/tools/peppol-validator)
- [Rule index](https://ironfang.com/docs/finance/rules.md)
- [Ironfang Finance API docs](https://ironfang.com/docs/finance)
- The same rule is available to MCP clients as the tool `finance.rule.get` on https://mcp.ironfang.com/mcp