Your question is Stock Order Book Matching. 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).
Make an order book for a commodity and match incoming buys with sells and vice versa.
Design the matching logic, data structures, and service boundaries for a real-time trading system. Focus on correctness under concurrency, ordering guarantees, latency, and how you would test and monitor the matcher in production.