If both supplier and customer are German, if "Payment means type code" (BT-81) contains a code for credit transfer (30, 58), "CREDIT TRANSFER" (BG-17) shall be provided.
(/ubl-invoice:Invoice/cac:PaymentMeans[normalize-space(cbc:PaymentMeansCode) = ('30','58')] | /ubl-creditnote:CreditNote/cac:PaymentMeans[normalize-space(cbc:PaymentMeansCode) = ('30','58')])[$supplierCountryIsDE and $customerCountryIsDE]cac:PayeeFinancialAccount