That's what I though too, maybe I'm missing something or I don't fully get it. But the human is always behind what's the difference if they go and sign up or tell an agent that they must sign up for you ?.
My best guess is that this a way of making a system talk to your agent without you knowing what they are talking about ? As a way of not exposing the real sign up method ?
Since it’s just used once, you can also just have an agent solve the captcha and then use the returned api key yourself. This has to be engagement bait.