Probably because the user took this particular asset offline. You can see what they're still offering on the YoYo marketplace right here:
Lonewolff GameMaker assets
Please notice that the user (on this forum at least) is either banned, or they deleted their account, as far as I can tell. So there's probably no way to contact them.
But fret not, for there's alternative solutions: if you're interested in text-to-speech (among many other things), look up "DLCEXT"
Well that's not been true for a long time at this point. Jeez, imagine if someone charged $9.99 for just
text-to-speech alone nowadays. Wouldn't that be horrible?
Despite several other things they said, that I don't agree with... this one is absolutely true. Unfortunately even more so for people who
know how to code C++ etc. but
still can't figure out how your stuff works, so they just give up and show strong signs of envy whenever they see you achieve something they couldn't manage to pull off themselves in the first place. It'll always be that way, sad as it is...
"Oh, I cannot fathom how you did the thing you did... and you never publicly released any documentation or source code, to allow me to steal parts of your code... so I'll just sh*t all over you for no reason to express my displeasure."
Developers (especially independent ones) should
support each other, for christ's sake; not see each other as "competition" to beat.