Wanted

So I have been looking out for job change having 7 yoe and mostly getting staff swe interviews. But in a recent interview I am a bit confused, having done good performance and having a solid discussion, I was rejected. Here how it went. I was asked to design promocode application system, and was given a basic design and asked to modify it. I did share many upgrades over current system, like Discussed and clarified requirements 1. introduction of caching 2. handling promocode validation 3. Discussed about storing of promocode 4. Handling of promocode expiry and updates I got a few followup like how to handle DDOS and other attacks- I answered it properly How would I test the system- i answered comprehensively Then second part was checking my code review style and capability - I was given a very basic code- i reviewed it and gave many suggestions based on SOLID principal, separation and modularising the code Handling exception better way, adding event ingestion But I was asked followup- 1. Is the return type sufficient for our use case- I had missed that but answered fully and along side refactored input as well and made the solution more extensible And the interviewer was showing engagement and saying good good ( now I understand that's his style, doesn't mean it). And after this I get a rejection email with very less feedback. Now I am confused, yes I might not be able to answer all and get all what he was thinking at once from my own, but if I am successfully able to answer what he asks, how can I still be rejected? No matter how much u try, there will be something u might miss yourself, but if u can answer when asked about, is this still a rejection?