I've experimented with influencer marketing before, mainly with Instagram Influencers for app downloads who would post a video I made for the app on their Instagram Stories, although the experience doesn't reflect paid candy subscriptions so it might not be as useful, this was also a small app I made on the side. I do remember getting 300 downloads from one influencer and the rest was negligible.

I figured out it was much easier to use young affluent females influencers from ages 18-25 who had 10000-15000 followers (not too much, as that dilutes the network and those who had too many followers were too expensive anyway) as they're usually super-connected in their network, "popular" and their followers (usually their friends, etc.) trust their opinions.

Interestingly, I didn't need to pay anything even though I didn't know these people, most were happy to just do it.

With Youtube, it would seem that only the big-name You-tubers are worth any kind of sponsorship. I find that influencer marketing is really about trust and credibility as your customer sales really come from trusting the influencer promoting the product and in turn also meeting that need the customer wanted too.