# DE-R-026

Source: https://xmlvalid.com/rules/DE-R-026

> If both supplier and customer are located in Germany, and if "Invoice type code" (BT-3) contains the code 384 (Corrected invoice), "PRECEDING INVOICE REFERENCE" (BG-3) should be provided at least once.

- Level: warning
- Rule sets: Peppol BIS Billing 3.0 rules 3.0.21
- Context: `(/ubl-invoice:Invoice | /ubl-creditnote:CreditNote)[$supplierCountryIsDE and $customerCountryIsDE]`
- Test: `((not(normalize-space(cbc:InvoiceTypeCode) = '384' or normalize-space(cbc:CreditNoteTypeCode) = '384') or (cac:BillingReference/cac:InvoiceDocumentReference)))`

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