Your question is Rate-Limiting System Design. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Design a rate-limiting / notification-style system (API + core classes).
Asked in the Low level design stage. Reported follow-ups: handling concurrency and edge cases, extensibility and trade-offs.