What it means
The buyer identifier (BT-46) is a number that identifies the buyer, for example the customer number you assigned or a GLN. In UBL it is cbc:ID inside the buyer's cac:PartyIdentification. The rule counts those elements and allows one. It is not the buyer reference (BT-10), where the Leitweg-ID of a German public-sector buyer goes, and it is not the buyer's electronic address (BT-49).
Why it matters
EN 16931 allows at most one buyer identifier per invoice or credit note.
How to fix it
In your invoicing software, open the customer record and check which identifiers it holds, such as a customer number and a GLN. Keep one in the field that is exported as the buyer identifier. Do not put the Leitweg-ID or a purchase order number here, they have their own fields. In the XML, keep one cac:PartyIdentification with one cbc:ID under cac:AccountingCustomerParty/cac:Party.
Once the file is corrected, check it again for free: Validate an invoice against EN 16931
Or fix the invoice in a form and download the corrected file, for 1 credit: Fix a rejected e-invoice
The rule as published
Buyer identifier shall occur maximum once Where this rule applies
| Rule set | Version |
|---|---|
| EN 16931 (UBL) | 1.3.17 |
| EN 16931 (UBL credit note) | 1.3.17 |
| XRechnung 3.0 (UBL) | 3.0.2 |
| XRechnung 3.0 (UBL credit note) | 3.0.2 |
| Peppol BIS Billing 3.0 (invoice) | 2026.5 |
| Peppol BIS Billing 3.0 (credit note) | 2026.5 |
| SI-UBL 2.0 / NLCIUS (invoice) | 2.0.3.13 |
| SI-UBL 2.0 / NLCIUS (credit note) | 2.0.3.13 |
| France CTC (UBL invoice) | 1.4.0-04 |
| France CTC (UBL credit note) | 1.4.0-04 |
| CIUS-RO UBL Invoice 1.0.9 | 1.0.9 |
| CIUS-RO UBL Credit Note 1.0.9 | 1.0.9 |
Check your file
Drop your e-invoice to see whether UBL-SR-16 still fails, and which other rules do.
Related rules
- UBL-SR-17 An invoice can have only one buyer company registration number
- UBL-SR-18 An invoice can have only one buyer VAT number
- UBL-SR-19 The payee needs one name, different from the seller's
- UBL-SR-20 The payee can have one identifier and must differ from the seller
- UBL-SR-21 A separate payee needs a different name and at most one registration number
- UBL-SR-22 A tax representative can have only one name