/ubl:Invoice | /cn:CreditNote[BR-B-02]-An Invoice that contains an Invoice line (BG-25), a Document level allowance (BG-20) or a Document level charge (BG-21) where the VAT category code (BT-151, BT-95, BT-118 or BT-102) is “Split payment" shall not contain an invoice line (BG-25), a Document level allowance (BG-20) or a Document level charge (BG-21) where the VAT category code (BT-151, BT-95, BT-118 or BT-102) is “Standard rated”.
Hitting this rule in production? Paste the invoice into the validator or wire the API into CI so it never ships broken again.