Revolut Software Developer interview questions

I think my interviewer for the live coding interview could have been better prepared. I implemented everything he asked for, but was rejected because I did not use mocks in the tests, and did not implement additional validations to my code, even though I constantly asked him if he had any other improvements in mind that I needed to implement. He expected me to guess what I needed to do instead of actually telling me? I was very communicative and open regarding my code, and somehow he did not asked me to create tests using mocks, so I assumed my tests that had 100% coverage were ok for the interview. Also, I was presented a problem I never encountered in my life (designing a load balancer) and since a lot of simplifications were made to the problem itself, I assumed that the validations I implemented were also ok. I asked lots of times if I was missing some validation, and was simply told "no, thats ok". Than the reasoning behind the rejection had this: "being open to adding validation logic when prompted would have improved robustness and demonstrated stronger ownership of edge cases and input safety."