There are a couple of threads about this topic. Here’s a recent one you can read for reference about the circumstances revolving around gambling:
While the mechanics you described are akin to a lootbox in that you are paying Robux to operate the machine and you always win an item, you need to make it explicitly clear that it is not a gambling machine and that’s just your way of representing your game’s depiction of lootboxes.
If you want to stay on the safe side of moderation, I wouldn’t recommend making a slot machine at all. They do take context and circumstances into account before making a decision but I’m no risk taker especially with Roblox moderation.
Whatever you end up choosing to create, make sure that the algorithm is completely random and fair to the player to be able to win items and that you’re disclosing the percentage change of winning anything through said machine.