Pre-flight a SEPA invoice's identifiers in one paid call: validate the customer VAT (VIES, with company name), the IBAN (ISO 7064 mod-97 + BBAN layout) and an ISO 11649 RF creditor reference, run together with a per-field status. summary.allProvidedValid is true only if every provided identifier checked out. If all provided checks fail technically you get a 503 and no charge. ?attest=1 → Ed25519-signed.