For Danish suppliers PaymentMandate/ID and PayerFinancialAccount/ID are mandatory when payment means is 49
ubl-invoice:Invoice[$DKSupplierCountry = 'DK' and $DKCustomerCountry = 'DK']/cac:PaymentMeansnot((cbc:PaymentMeansCode = '49')       and not((normalize-space(cac:PaymentMandate/cbc:ID/text()) != '')           and (normalize-space(cac:PaymentMandate/cac:PayerFinancialAccount/cbc:ID/text()) != ''))       )