Sorry for the poor explanation, English isn't my primary language. Thank you for responding so quickly. Perhaps because I've been playing for so long, I've somehow forgotten how they were connected, since a couple of days have passed since that save.
And another pretty funny thing:
You can't buy a level for 0 coins if you have 0 coins in your pocket (I don't remember the NPC's name). The same thing works with items in the store.