(probably not going to help you answer your question)

I am going to rewrite this whole script. I will split it into three parts.

1. Client script

This will be the client script

local RS = game:GetService("ReplicatedStorage")
local RollEvent = RS:WaitForChild("RollEvent") -- Wait for event
local RollButton = script.Parent -- Put this script inside the button

RollButton.Activated:Connect(function()
    RollEvent:FireServer("Common")
end)

2. Replicated event

You will need to create a replicated event in order for this to work

1. Scroll to ReplicatedStorage in explorer
2. Insert a RemoteEvent in ReplicatedStorage
3. Rename the RemoteEvent to RollEvent

If you don't follow the above instructions, your code will break

3. Server script

This will be the server script

--[[
Case script by TTChaos

["Item Name"] = {Location = Location, Rarity = 50}, 
Rarity is optional, Location is necessary
--]]

local CommonCase = workspace.CommonCase -- Common Case Location
local RS = game:GetService("ReplicatedStorage")
local RollEvent = RS:WaitForChild("RollEvent")

local CommonCaseItems = {
    ["Sabre"] = {Location = CommonCase.Common.Sabre}, 
    ["Axe"] = {Location = CommonCase.Common.Axe},
    ["Crowbar"] = {Location = CommonCase.Common.Crowbar},
    ["Axe 2"] = {Location = CommonCase.Common.Axe2}, -- Name it something better
    ["Fife"] = {Location = CommonCase.Common.Fife},
    ["Combat Knife"] = {Location = CommonCase.Common["Combat Knife"]},
    ["Machete"] = {Location = CommonCase.Common.Machete},
    ["Lance"] = {Location = CommonCase.Common.Lance},
    ["Chistmas Tree Sword"] = {Location = CommonCase.Rare.ChristmasTreeSword},
    ["Hyper"] = {Location = CommonCase.Epic.Hyper},
}

local RareCaseItems = { -- Example
    ["Christmas Tree Sword"] = {Location = CommonCase.Rare.ChristmasTreeSword}
}

function DetectRarity(Player, Rarity) -- Define the function
    if Rarity == "Common" then
        if PlayerCanAfford(100, Player) then
            RollCase(Player, CommonCaseItems) -- Roll case
        end
    elseif Rarity == "Rare" then
        if PlayerCanAfford(250, Player) then
            RollCase(Player, RareCaseItems) -- Example
        end
    end
    print("Finished!\n")
end

--[[
Please do not change anything below this comment
Changing anything below this comment will break the script
--]]

function PlayerCanAfford(Price, Player) -- Function to deduct cash
    if Player.leaderstats.Cash.Value >= Price then
        Player.leaderstats.Cash.Value -= Price
        return true
    else
        return false
    end
end

function RollCase(Player, CaseRarity)
    local Counter = 0  -- Roll a random number between 1 and 100
    local RandomChoice = math.random(1, 100)
    for ItemName, ItemProperties in pairs(CaseRarity) do -- Loop through items
        local ItemRarity = ItemProperties["Rarity"] or 100/#CaseRarity -- Assign rarity
        if (RandomChoice > Counter) and (RandomChoice <= Counter + ItemRarity) then -- Detect if Item was rolled
            print(string.format("You got a %s! The chances of getting one is %u%%!", ItemName, ItemRarity))
            AwardItem(Player, ItemName, ItemProperties["Location"])
        else
            print(string.format("No, the item is not a %s.", ItemName))
        end
        Counter = Counter + ItemRarity
    end
end

function AwardItem(Player, ItemName, Location) -- Simple award script
    local ItemClone = Location:Clone()
    ItemClone.Parent = Player.Backpack
end

RollEvent.onServerEvent:Connect(DetectRarity)

Edit: Doesn't deduct the coins