Field AI Fullstack Developer interview questions

I literally turned down working with them because after chatting with them it seemed very startup-y I wasn’t looking to do startup life again, but they messaged me back a week after I turned them down to try to convince me to apply anyway. I say why not if they’re that interested? I tell them I’m full stack but I’m heavily FE specialized. They say that’s fine, that’s exactly what they’re looking for. They then bring me back in for a 4 hour slog just to end with an entirely back end system architecture question. I struggle through because - once again - I’m not a back end specialist and I kept saying I wasn’t. I get turned down purely because I wasn’t strong enough on the back end. Extremely frustrating to say the least. I was very upfront with my skillset - they were not upfront with what they wanted. I wish them luck in finding whatever it is they’re trying to find, I dont think they know what that is though