From 2026 a rejected invoice is no longer an unanswered email. It's a document the platform refuses to accept as issued: Peppol in Belgium, KSeF in Poland, mandatory reception in France.
Under clearance, failed validation means the invoice never existed. So validate at your own desk, and fail with the rule id and the element path, not a generic 500. You probably want to know where your invoice pipeline currently finds out it was wrong. https://shipmindlabs.com/c/e2a2f004