If the group "DIRECT DEBIT" (BG-19) is delivered, the element "Debited account identifier" (BT-91) shall be provided.
(/ubl-invoice:Invoice | /ubl-creditnote:CreditNote)[$supplierCountryIsDE and $customerCountryIsDE]
not(cac:PaymentMeans/cac:PaymentMandate) or (cac:PaymentMeans/cac:PaymentMandate/cac:PayerFinancialAccount/cbc:ID)