How do I fix UBL-SR-39?

Keep one project reference: PRJ-2026-014 .

Peppol BIS Billing 3.0 · rule

UBL-SR-39

Layer en16931·Checked against Peppol BIS Billing 3.0 2026.5

What does UBL-SR-39 mean? Project reference shall occur maximum once.

Why did my invoice fail UBL-SR-39?

The Project reference (BT-11) identifies the project the invoice relates to. EN 16931 allows at most one project reference per invoice, so cac:ProjectReference/cbc:ID must not appear more than once at document level. Use additional document or contract references for other linkage rather than repeating the project reference.

Official rule text

Project reference shall occur maximum once.

Common causes

Two cac:ProjectReference blocks at document level.
cbc:ID repeated inside a single cac:ProjectReference.
A multi-project invoice modelled with several project references instead of separate invoices.

How do I fix it?

Keep one project reference: <cac:ProjectReference><cbc:ID>PRJ-2026-014</cbc:ID></cac:ProjectReference>.

Check your invoice against this rule

Paste it into the live demo, or call POST /v1/validate. See the quickstart.