The orders nobody knew were unpaid

An upstream ERP outage left a set of orders that were never invoiced. Nothing looked broken. The site kept trading, no error page, no alert. It was revenue quietly not collected, which is the worst shape a bug can take: it does not announce itself and it does not stop.

I traced it to how the integration behaved when the ERP was unavailable at the invoicing step. The code assumed an answer would always come. I shipped a fix so the flow degrades safely instead of dropping the order, then wrote and ran a repair over the records already affected, and reported the finding and the remediation to the client and the product managers myself.

Revenue that would have been lost was recovered, and the failure mode cannot recur silently. It is the clearest example of how I think about third-party systems: assume they will fail, and design so that failure is loud and recoverable.