As I understand, the "work" was already done, the only thing missing was sending a heads-up email with "hey, this seems iffy, maybe you ought to look into it".
I dunno, I generally report issues I find in software, paid or not, as I've always done. Takes usually ~10 minutes and 1% of the time, they ask for more details and I spend maybe 20 minutes more to fill out some more details.
Never been paid for it ever, most I gotten was a free yearly subscription. But in general I do it because I want what I use to be less buggy.