How do I validate IČO + DIČ in Magento? What about ARES + VIES?

Two Czech B2B identifiers, two different validators:

• IČO (Identifikační číslo osoby), 8-digit company ID. Issued by the Czech Statistical Office. Validated against ARES (Administrativní registr ekonomických subjektů), the free Czech business-registry API run by the Ministry of Finance.
• DIČ (Daňové identifikační číslo), VAT-ID, format CZ + 8 to 10 digits (often CZ + IČO for companies). Validated via VIES VAT (EU-wide) for cross-border B2B.

For Magento B2B we:

1. Add IČO + DIČ fields to the customer entity (or B2B company on Adobe Commerce).
2. Hit ARES on registration / address-change, rejects invalid / dissolved companies, auto-fills company name + registered address + legal form (s.r.o. / a.s. / OSVČ).
3. Validate DIČ against VIES for cross-border zero-rated B2B sales (intra-EU reverse charge).
4. Apply 0% DPH on B2B intra-EU sales with a valid VIES-validated DIČ (reverse charge); standard 21% on B2C and CZ→CZ B2B.
5. Cache validations 30 days, re-validate on any address change.