It’s hard to tell exactly what the author said… someone whose English isn’t amazing, talking to somebody else whose English isn’t amazing leaves plenty of room for misinterpretation.
For example… you’re taking “no, only API” to mean that “no, this item only contains an API system” whereas it could mean “no, only my API item can do that, and this item can’t” just as an example. It’s hard to tell exactly what he’s saying. I mean, his first response was to check the description as it gives all the details… does the description mention anything about an API?
And if the item doesn’t contain an API then that’s not something that would be covered by support anyway. Support is just to make sure the item is working as it should, plus a bit of advice on usage here and there… it’s not to edit or add new features.
Don’t get me wrong, if I was the author and I was in the same position, I’d give you a refund under the circumstances… but I’m just pointing out that it’s unlikely the author was trying tk blatantly lie to you. It’s more likely this was just a bit of a mix up.