KYC Onboarding Validation Checklist — IBAN, LEI & VAT in One Flow (Python)

Three identifiers, three API calls, one onboarding flow. Here's how to validate a counterparty's IBAN, LEI, and VAT number before opening an account — and why skipping any of them is a compliance risk. Table of contents What is KYC and why validation matters The three identifiers Step 1: Validate the IBAN Step 2: Validate the LEI Step 3: Validate the VAT number Putting it all together — parallel validation cURL examples Handling failures gracefully Summary checklist 1. What is KYC and why validation matters KYC (Know Your Customer) is the process of verifying the identity of a counterparty before entering a business relationship. Regulations like AML4/AML5 (EU Anti-Money Laundering Directives), the Bank Secrecy Act (US), and MiFID II require financial institutions to verify key identifiers at onboarding — not as a formality, but as a legal obligation with real consequences for non-compliance. Three identifiers form the backbone of entity KYC in Europe: IBAN — confirms the bank account