/ubl:Invoice/cac:AllowanceCharge[cbc:ChargeIndicator = false()] | /cn:CreditNote/cac:AllowanceCharge[cbc:ChargeIndicator = false()][BR-33]-Each Document level allowance (BG-20) shall have a Document level allowance reason (BT-97) or a Document level allowance reason code (BT-98).
Hitting this rule in production? Paste the invoice into the validator or wire the API into CI so it never ships broken again.