Continuing and highlighting a side discussion from another thread: No Heart of Rage Support Group - #34 by sls
What are the drop rates for the Vault?
Since vault keys can be purchased with real money, the rates need to be public as per the agreements with Google, Apple, Amazon, Sony, Nintendo, and Microsoft.
Here’s Google Play Store’s policy: Payments - Play Console Help
Apps and games offering mechanisms to receive randomized virtual items from a purchase including, but not limited to, “loot boxes” must clearly disclose the odds of receiving those items in advance of, and in close and timely proximity to, that purchase.
Currently in game, you can buy vault keys and use that to start a vault battle and get random rewards (a loot box).
Edit: Proof the game sells vault keys, aka loot boxes. This is fine to do, but drop rates must be disclosed.