Card payment authorization and routing

Design a card payment gateway that authorizes ~8,000 transactions/sec at peak across 4 acquiring banks, routing each charge to the cheapest/most-likely-to-approve PSP. Each authorization must be exactly-once toward the bank (no double-charge) even when the merchant client retries, and the merchant needs a synchronous approve/decline within 2s p99. Walk the components, the data model, and how you guarantee no double-authorization under client retries and partial network failures.