This is normally not something worth doing after just an initial phone call, but I went for it because I liked the people I interviewed with and the opportunity. However, the project utilized an API that was terrible. Beyond bad, worse than any API that you would ever encounter in production. No querying, no way around MANY API calls for simple tasks. But hey, a good challenge - I'm happy to take it on. I submit the project and then simply get back a "We have decided not to move forward at this time" - Nothing specific about the project, nothing about me as a candidate, nothing. Hours on a project, zero feedback and a rejection.