First of all, I am sorry for what happened to ethereal, it's obvious he’s the victim as he’s the one who lost the money. It was my fault that this happened as it was my API that got compromised. I logged into shady website with my steam login, so the scammers gained access to every trade that I do.
In case anyone is wondering how that is possible, this video explains how:
Secondly, I believe my initial reaction to what happened was incorrect, not only did I promise that I would repay him in full (despite the fact that I was not the person responsible for the scam and gained nothing from it) I also continued to engage with him and keep promising him that I would pay some of it. The truth is I simply forgot to do it and when he asked me again, I did not have the amount of keys in my inventory at that particular moment of time. That was my fault entirely.
I am aware I was being sarcastic in my replies to him, but everyone who knows me personally knows that's just how I react to things. I realize what I said sounded immature but I never meant it as malicious and I am sorry that he misinterpreted that.
As I had already told him, the new highlander season starts in January, and then I will be able to reimburse him in full (35 keys).
I learned a lot from this situation, and I acknowledge my lack of due diligence led to this situation unfolding the way it did.
I promise I will be a lot more cautious with future item signings.