Design real-time payments fraud model under constraints

You are designing a production machine learning system for real-time checkout on a large gaming platform. The goal is to reduce unauthorized purchases made by minors using a parent’s payment card. For each checkout attempt, the system must choose exactly one of the following actions: allow, step-up auth (e.g., CVV or SCA), hold-for-review, or block. Every decision must be returned within a 30 ms p99 latency budget. Your response should explicitly address the following…