Regarding the difference in information from my post and the other post: this is because they’re treated as two different scenarios. If there’s an 100% guarantee to win an item then it falls under a different policy that does allow purchase of currency but the exact chances must be disclosed.
I have a more detailed post regarding gambling and the differing policies in the thread below:
I strongly encourage any future readers not to take advice here that just says “many games do it so it’s fine” because if they aren’t in compliance with the rules then you’re adding to the pile of non-compliant games that are liable for moderation action.