NestJS Real Time Fraud Detection, Catching Suspicious Transactions Before They Clear

Short summary

Instant payment rails like FedNow and RTP require fraud detection to run synchronously before settlement, eliminating the luxury of post-settlement batch review. This article demonstrates a NestJS architecture using composable fraud rule interfaces and an interceptor pattern to evaluate transactions in real time. Each rule (unusual amount, velocity) returns a risk score, and the interceptor aggregates scores before allowing the payment to proceed.

• •Instant payments force fraud detection into the transaction path, not after
• •NestJS interceptor pattern runs composable fraud rules before settlement
• •Each rule returns a risk score; interceptor aggregates and decides whether to block

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