As posed, I don't think this question is "answerable", but here are some thoughts that may be helpful for you in future interviews.
In my experience (both as an interviewee as well as interviewer), the actual "answer" the interviewee provides to this type of question isn't really that important. What you're being tested on with a question like this is broadly "design thinking" as well as how you approach problems.
Without knowing a lot more of the specifics, it would be impossible to provide a reasonable system design that would accomplish the goals of the people using it. IMHO that's the point of this type of question: to see what you ask and how you approach it.
Sure, the interviewer said, "Don't worry about how the fraud detection stuff actually works", which is totally reasonable. But the first place to start is by asking questions.
For example, my first question would be something like this:
What do you mean by "analytics"? Analyzing how well the deployed system is performing in terms of latency / stability? Or understanding the actual "performance" of the model (e.g. correct / incorrect fraud detection)?
Depending on the answer given by the interviewer, a ton of different followup questions might be relevant. Once you've asked enough questions to more or less understand the goals, it might be more clear what a "good" system design would be.
However, as I've already said, I don't think the system design you end up with needs to be perfect or absolutely ingenious. I really do believe that the portion of the interview where you're trying to uncover the parameters of the problem is the part that matters more. After all, that's a pretty important part of the job :)