The element "Invoice type code" (BT-3) should only contain the following values from code list UNTDID 1001: 326 (Partial invoice), 380 (Commercial invoice), 384 (Corrected invoice), 389 (Self-billed invoice), 381 (Credit note), 875 (Partial construction invoice), 876 (Partial final construction invoice), 877 (Final construction invoice).
(/ubl-invoice:Invoice | /ubl-creditnote:CreditNote)[$supplierCountryIsDE and $customerCountryIsDE]cbc:InvoiceTypeCode = $supportedInvAndCNTypeCodes or cbc:CreditNoteTypeCode = $supportedInvAndCNTypeCodes