Under Roblox's Terms of Use, if you offer randomized virtual items that users can purchase with Robux or other in-experience currency, you must indicate all the actual numerical odds of what they may receive. For example, if a user has the opportunity to purchase a magic charm that has the random chance to either have a rare, epic, or legendary status, you must disclose the odds of their potential award before they spend Robux:
This policy also applies to indirect purchases. For example, if a user uses their Robux to purchase a seed, then later plants the seed in exchange for a randomized virtual item, you must disclose the odds of their potential award before they plant the seed.
If your experience offers randomized virtual rewards in exchange for completing an action that does not involve the payment of Robux or other in-experience currency, you aren't required to disclose the odds. For example, if a user locates a key that opens a treasure chest, you don't need to state the odds of what items they might receive from the treasure chest.