Revolut Senior Java Developer interview questions

The first step is to do a home assignment. They asked to do a small RESTful service about banking without many details. I hope they understand that candidates for senior positions are working people, not students. And time that could be dedicated to such assignments is limited. I composed a very basic API and focused on performance, which is my specialization. They replied that the code has poor readability and misuses HTTP methods (actually, REST doesn't say anything about the use of HTTP methods, look it up) and contains too few tests. Well, of course I could've done better, if I invested more time. But the assignment didn't say anything about criteria.