# DE-R-027

> If both supplier and customer are located in Germany, "Seller contact telephone number" (BT-42) should contain a valid telephone number. A valid telephone should consist of 3 digits minimum.

Checked against Peppol BIS Billing 3.0 2026.5

Canonical: https://einvoicecheck.eu/rules/de-r-027

## Official rule text

If both supplier and customer are located in Germany, "Seller contact telephone number" (BT-42) should contain a valid telephone number. A valid telephone should consist of 3 digits minimum.