[IBR-073-OM] - Either both or neither Allowance base amount (IBT-137) and percentage (IBT-138) MUST be provided.
IBR-073-OMubl:Invoice/cac:InvoiceLine/cac:AllowanceCharge | cn:CreditNote/cac:CreditNoteLine/cac:AllowanceCharge(cbc:BaseAmount and cbc:MultiplierFactorNumeric) or (not(cbc:BaseAmount) and not(cbc:MultiplierFactorNumeric))