# DE-R-027

Source: https://xmlvalid.com/rules/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.

- Level: warning
- Rule sets: Peppol BIS Billing 3.0 rules 3.0.21
- Context: `(/ubl-invoice:Invoice/cac:AccountingSupplierParty/cac:Party/cac:Contact | /ubl-creditnote:CreditNote/cac:AccountingSupplierParty/cac:Party/cac:Contact)[$supplierCountryIsDE and $customerCountryIsDE]`
- Test: `matches(normalize-space(cbc:Telephone), $XR-TELEPHONE-REGEX)`

Validate a document against these rules: https://xmlvalid.com/validate