cac:InvoiceLine/cac:InvoicePeriod | cac:CreditNoteLine/cac:InvoicePeriod[BR-30]-If both Invoice line period start date (BT-134) and Invoice line period end date (BT-135) are given then the Invoice line period end date (BT-135) shall be later or equal to the Invoice line period start date (BT-134).
Hitting this rule in production? Paste the invoice into the validator or wire the API into CI so it never ships broken again.