I don't know the answer either so I put in on the Discord in the hopes that someone there will know [we also have the devs there and they read through sometimes]. Unfortunately wikia discussions aren't very active >.>
Unfortunately though it didn't go as well as [*insert absolute answer here*] but I got a "[You] can contact the devs. If all of the friends are willing to provide a couple screenshots they will give you minty" because no-one can find what you did wrong, it really just seems like some sort of glitch. (No response from the devs, but their summer break ends in ~4 days)
[If you're unsure how to contact them email "firstname.lastname@example.org", and if you've never spoken to them before they were really nice to me, the first time the responses where pretty slow (not a complaint, there's not many of them) but it was faster later.]
Good luck! I hope you get Minty Heart. And if you need any more help please ask!