The Time I Wrestled With Money That Vanished (And How I Fixed It)

August 18, 2024

A few months ago, I worked on an escrow system for a fintech startup—a place where money sits patiently until two people agree it should move. Sounds simple, right? Until one day, we started seeing payments vanish. Not literally, but close enough: funds would get “stuck,” double-allocated, or just plain lost. Turns out, we had race conditions—a fancy term for when two processes fight over the same money at the same time, like two people trying to grab the last cookie.

Here’s the thing: money can’t afford to be messy. If Alice pays Bob through escrow, that cash has to move exactly once, and only when both agree. But Stripe, the payment tool we used, works asynchronously. It’s like mailing a check instead of handing over cash—you send it, but you don’t know it’s done until the recipient cashes it. That delay created gaps where our app could get confused. Did the payment succeed? Fail? Is it still floating in the void? I spent nights staring at logs where two servers tried to release the same funds at the same time. It felt like trying to catch smoke. So I built a “traffic light” system. Every time Stripe’s API said a payment was done (via webhooks—little notifications Stripe sends), I’d put a database lock on that escrow account. Think of it as a “Do Not Touch” sign. Inside that lock, I’d check: Did both parties actually agree? Are all conditions met? Only then would the money move.

But even that wasn’t foolproof. Databases can be sneaky. So I wrapped everything in transactions—database speak for “all-or-nothing.” If one step failed, the whole process rolled back, like undoing a bad chess move. And I made sure Stripe’s webhooks were handled idempotently, meaning if they sent the same message twice (which they often did), we wouldn’t panic. We’d just shrug and say, “Yeah, we already did that.”

The day we deployed this wasn't exactly one of my best days, even though I am normally cool headed about issues. But the race conditions stopped. Money flowed cleanly. It wasn’t glamorous or fancy algorithms, just careful locks and double-checking—but it worked. I learned that sometimes, the hardest problems aren’t about being clever. They’re about being stubborn. You have to out-wait the chaos, close every gap, and never assume the system will behave. Because money, like people, hates uncertainty. And in the end, all it wanted was a little clarity.

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