For a fun time, ask an accountant how to recognize revenue for this purchase. (Gems are a premium in-game currency available at a variety of price points including, most relevantly, $10 for 1.5k gems.)
Even if transferable to other players, ToS usually states that you don't ever actually own anything you earn in the game so no problem. If this was crypto Game-Fi and you actually did get ownership of transferable gems or whatever, we have to ask a bunch more questions.
just saw the rest of the thread. Yeah, I can see how from the game dev's perspective, accounting for this could be a nightmare. Probably want to add some fast decay feature to an abandoned bank so you can wipe those unused balances out!