You aren’t able to lose currency from unboxing loot: you are always guaranteed an item. Roblox treats this as a separate case to gambling and has guidelines in place for this as well.
In the case of crates, if Robux is involved at any step of the process, you are required to add full percentage disclosure about the rarities or chances of getting items in each box. Akin to gambling as well, there must be no algorithm which skews chance, hence full disclosure.
I’ve also made a response to a topic specific to percentages and crates, if you’re interested. See here: