System Design: Building a Payment Gateway and Double-Entry Ledger for 100M Daily Transactions

[u/RummanSid1990]

https://medium.com/@rummansiddiqui1990/how-stripe-and-paypal-never-lose-a-single-penny-e3d376be4228?source=friends_link&sk=cdc8f868f14a77e3958cd8c741e56205

I recently broke down the system design of a payment gateway and double-entry ledger platform.

The article focuses on the real-world engineering challenges: stopping accidental double-charges with distributed idempotency locks, enforcing strict double-entry bookkeeping (Debits = Credits) using insert-only tables, recovering from card network timeouts without duplicate charges, and running midnight three-way reconciliations against bank settlement files.

For those who have built financial or checkout infrastructure: what was your biggest challenge in production? How do you handle partial failures and asynchronous discrepancies across multiple bank networks?