How We Caught Fraud Before the Payment Cleared

I want to tell you about the day our fraud system started losing. Not to fraudsters. To the clock. We had built what looked, on paper, like a solid fraud detection pipeline. An in-house ML model trained on months of transaction data, a feature store we were proud of, a scoring service sitting neatly between checkout and payment authorisation. Fraud catch rates were good. The data science team was happy. Then we scaled past a million transactions a day, and everything started to crack. Not in an