Did it totally tank the whole deal or did they just ghost after? That stings either way, $600 is real money. I did something kind of similar once where I let a template reply go out with the wrong name in it and the person noticed right away. Nothing kills trust faster than feeling like you got a copy paste job, even if you spent an hour on it. Next time maybe run it through your own words before it goes out, just so it sounds like a person. Hope that client comes back around.