Validation rules

BR-CO-04 — EN 16931 rule

An invoice line is not categorized with a VAT category code (BT-151).

Rule

BR-CO-04 — official EN 16931 / XRechnung rule

Severity

error

Business term

BT-151 — Line VAT category

Field in your JSON

invoice.lines[*].vat_category

Detected by

tier 3 — KoSIT validator (authoritative)

Reachability

Only reachable when validating your own XML — normbill-generated documents cannot trigger it

The engine derives a category for every line it serializes; a line with neither vat nor vat_category is stopped at tier 1 (NB-VAT-RATE) before generation.

How to fix it

Add cac:ClassifiedTaxCategory with a UNCL 5305 code (S, Z, E, AE, K, G, O, L, M) to the line's cac:Item.

Related rules

• BR-O-11 — VAT category "O" (not subject to VAT) cannot be mixed with other VAT categories on the same invoice…
• BR-AE-01 — Lines or document-level allowances/charges use VAT category "AE" (reverse charge), so the VAT breakdown…
• BR-B-01 — VAT category "B" (Italian split payment) is only allowed on domestic Italian invoices — every country code…
• BR-B-02 — VAT category "B" (Italian split payment) must not be combined with category "S" (standard rated) on the same…
• BR-E-01 — Lines or document-level allowances/charges use VAT category "E" (exempt), so the VAT breakdown (BG-23) must…
• BR-G-01 — Lines or document-level allowances/charges use VAT category "G" (export outside the EU), so the VAT…

Official sources

• XRechnung specification (KoSIT / xeinkauf.de)
• KoSIT validator on GitHub and the XRechnung validator configuration

Every 422 from the API lists the rule id, the path in your request JSON, a plain-language message and a suggested fix — see the docs overview for the report format.

Or try it live: drop any XRechnung XML on the free validator — same KoSIT-backed report, no account.