The specification identifier is not the XRechnung one
`Specification identifier` (BT-24) should carry the URN of the XRechnung standard: the CIUS, its extension, or the CVD profile.
Only the issuer holds this value: Factlint reports it and never fabricates it. Test your invoice to find out whether it is affected.
The message your validator prints
Copied verbatim from the sealed artefact: this is the exact sentence the check prints when this rule fails.
[BR-DE-21] Das Element "Specification identifier" (BT-24) soll syntaktisch der Kennung des Standards XRechnung entsprechen.
Quoted from schematron-xrechnung 3.0.2, licensed under Apache-2.0.
Common searches around this code
These phrases mirror what an integrator searches for: code, syntax, rule, business field and correction.
Test your file with this error in mind
Upload the invoice involved: the report will say whether this code appears, where it appears in the document, and whether Factlint can only report it or also fix it.
To automate this check in an ERP flow, call the validation API and link every returned code to its public page.
Why this error happens
The common case is not a missing URN but a stale one — from an earlier XRechnung version, or the bare EN 16931 URN. The document is then judged against rules it does not claim to follow, which explains findings that seem to come out of nowhere.
How to fix it
Have your generator write the expected URN. Factlint does not replace it, even though only one value is correct: rewriting BT-24 would make the document *declare* conformance to a CIUS its issuer never claimed. That is what separates this case from `BR-01`, where a missing URN follows from what the document actually contains.
XML correction example
<ram:ID>urn:cen.eu:en16931:2017</ram:ID>
<ram:ID>urn:cen.eu:en16931:2017#compliant#urn:xeinkauf.de:kosit:xrechnung_3.0</ram:ID>