Not Changing Value of Cash if Gamepass?

I believe these scripts will work as you want to. Although I can not promise anything. Please tell me if and what the errors are and I will try to fix it.

Local Script

local player = game.Players.LocalPlayer
local cash = player:WaitForChild("leaderstats").Cash
local id = 8068400
local remEvent = game.ReplicatedStorage.GamePass -- Change this to the name of your RemoteEvent
local secondRemEvent = game.ReplicatedStorage.BuyGamePass -- Change this to the name of your second RemoteEvent
local label = script.Parent

remEvent:FireServer(id)

secondRemEvent.OnClientEvent:Connect(function(succes) -- The "player" argument is only to tell which player who should recieve the signal
    if succes then
        cash.Value = "9999999999"
        label.Text = "Infinite"
    end
end)


remEvent.OnClientEvent:Connect(function(ido, purchased) -- The "player" argument is only to tell which player who should recieve the signal
    if purchased and ido == id then
        wait(1)
        cash.Value = "9999999999"
        label.Text = "Infinite"
    else
        label.Text = "cash.Value"
    end
end)

Server Script

local service = game:GetService("MarketplaceService")
local remEvent = game.ReplicatedStorage.GamePass -- Change this to the name of your RemoteEvent
local secondRemEvent = game.ReplicatedStorage.BuyGamePass -- Change this to the name of your second RemoteEvent
local succes = false

remEvent.OnServerEvent:Connect(function(player, id) -- The player argument is sent automatically when a Client fires a RemoteEvent
    if service:UserOwnsGamePassAsync(player, id) then
        succes = true
        secondRemEvent:FireClient(player, succes)
    end
end)

service.PromptGamePassPurchaseFinished:Connect(function(player, id, purchased)
    remEvent:FireClient(player, id, purchased)
end)

Edit: You should create two RemoteEvents and place them in ReplicatedStorage. Place the Server Script in ServerScriptService. And just change the code in the LocalScript you already had. Please respond with the error if it's not working.

So, the reason it won’t change is because leaderstats cannot be changed on the client due to filtering enabled. Create a remote event in ReplicatedStorage and call it ChangeMoney, then write this code

LocalScript

local player = game.Players.LocalPlayer
local gamePassId = 8068400
local MPS = game:GetService("MarketplaceService")
local RS = game:GetService("RunService")
local Event = game:GetService("ReplicatedStorage"):WaitForChild("ChangeMoney")

while RS.Heartbeat:Wait() do
    if MPS:UserOwnsGamePassAsync(player, id) then
       Event:FireServer(math.huge)
       script.Parent.Text = "Infinite"
    else
        script.Parent.Text = cash.Value
    end
end

MPS.PromptGamePassPurchaseFinished:Connect(function(plr, ido, hasPurchased)
    if hasPurchased and ido == gamePassId then
        wait(1)
        Event:FireServer(math.huge)
        script.Parent.Text = "Infinite"
    else
        script.Parent.Text = cash.Value
    end
end)

ServerScript

local Event = game:GetService("ReplicatedStorage"):WaitForChild("ChangeMoney")

Event.OnServerEvent:Connect(function(plr, value)
    plr:WaitForChild("leaderstats").Cash.Value = value
end)