Credit Genie Software Engineer Interview Experience — FastAPI CRUD Pairing, Rejected Over a Communication Slip

When I was preparing, I couldn't find this question on the forum — it's a startup, so that's understandable. Here's the overall process:

• Hiring Manager Interview
• Technical Pairing, Python
• AI/ML Technical Pairing
• Systems Architecture & Design (AI/ML)
• Motivation + Mission Alignment
• Executive Interview

I got cut after the first round, which combined the Technical Pairing and the Hiring Manager Interview. This role leans toward new grads from CMU; I'm not from CMU but somehow still landed an interview. The interviewer had a PhD from CMU and senior MLE industry experience.

At the start, they introduced the company, introduced themselves, then had me introduce myself, and then we moved to a codepad for the coding part. First they gave a simple Python question — write a function that prints a few lines of numbers, then asked me about the time/space complexity.

Then they asked if I had used FastAPI. I said no, and the interviewer said that was fine, then laid out the actual problem: based on two functions they'd already provided as a framework, mimic them and write two more functions (basically the four CRUD functions — create, delete, query, update). It was my first time writing FastAPI, but I copied and adapted what was already there and got it working. After that, the interviewer handed me the Chroma documentation and had me add Chroma on top of the original CRUD code. The whole thing was collaborative — talking it through with the interviewer while writing the code together.

Where I think I completely bombed: while writing the last search-query function, there was a spot where I needed to return a specified object, just an empty one. I said "return empty," which didn't come out clearly — the interviewer thought I meant returning None directly, when actually the function was supposed to return the specified output object, just with an empty list inside it. The interviewer ended up walking me all the way back to the class definition from the very beginning, and we spent a long time on it. I got confused too, thinking: if the search doesn't find anything, can it even return something else? In the end it came down to a communication gap, or really, me not expressing myself clearly. I did eventually get the code working. After that came the candidate-questions part, and once I'd asked a few the interview wrapped up. Two hours later I got the rejection.

I'm not sure if there was something else I did wrong, and I'd appreciate it if people here could help me review this. I've been job hunting for 7 months now and I'm pretty numb to it at this point. Before this I interviewed at a big company for a DS role, answered all 5 rounds of questions, and still got rejected. That completely broke me. I don't even know what went wrong anymore.