/ubl:Invoice/cac:AllowanceCharge[cbc:ChargeIndicator = true()] | /cn:CreditNote/cac:AllowanceCharge[cbc:ChargeIndicator = true()][BR-38]-Each Document level charge (BG-21) shall have a Document level charge reason (BT-104) or a Document level charge reason code (BT-105).
Hitting this rule in production? Paste the invoice into the validator or wire the API into CI so it never ships broken again.