Each Invoice line allowance (ibg-27) shall have an Invoice line allowance reason (ibt-139) or an Invoice line allowance reason code (ibt-140).
//cac:InvoiceLine/cac:AllowanceCharge[cbc:ChargeIndicator = false()] | //cac:CreditNoteLine/cac:AllowanceCharge[cbc:ChargeIndicator = false()]
exists(cbc:AllowanceChargeReason) or exists(cbc:AllowanceChargeReasonCode)