# UBL-SR-08

> Invoice period shall occur maximum once

Checked against Peppol BIS Billing 3.0 2026.5

Canonical: https://einvoicecheck.eu/rules/ubl-sr-08

## Official rule text

Invoice period shall occur maximum once

## Why did my invoice fail UBL-SR-08?

The Invoice period group (BG-14), which defines the invoicing period start (BT-73) and end (BT-74) dates the invoice covers, may occur at most once at document level. In UBL this is the header cac:InvoicePeriod, and only one such period is allowed for the whole invoice.

## Common causes

- A header cac:InvoicePeriod is emitted more than once, e.g. one for start and one for end.
- Line-level periods are accidentally serialized at document level.
- Billing spans multiple periods and each is added as a separate header InvoicePeriod.

## How do I fix it?

```
Use one header period: <cac:InvoicePeriod><cbc:StartDate>2026-06-01</cbc:StartDate><cbc:EndDate>2026-06-30</cbc:EndDate></cac:InvoicePeriod> and place any distinct per-line periods under cac:InvoiceLine/cac:InvoicePeriod instead.
```