Why won't marketplace service work?

i see your script. if youre using a gamepass:

local productId = 1138688305
game.Players.PlayerAdded:Connect(function(player)
    Game:GetService("MarketplaceService"):PromptProductPurchase(player, productId)
end)

if its a devproduct:

local MarketplaceService = game:GetService("MarketplaceService")
local Players = game:GetService("Players")

local productID =  1138688305 -- Change this to your developer product ID

-- Function to prompt purchase of the developer product
local function promptPurchase()
    local player = Players.LocalPlayer
    MarketplaceService:PromptProductPurchase(player, productID)
end

after that you need to insert another script in serverscriptservice if youre using a devproduct to get the robux... you forgot that. but you have to add a benifit for that donation. how about 1 gold(lol)?

local MarketplaceService = game:GetService("MarketplaceService")
local DataStoreService = game:GetService("DataStoreService")
local Players = game:GetService("Players")

-- Data store for tracking purchases that were successfully processed
local purchaseHistoryStore = DataStoreService:GetDataStore("PurchaseHistory")

-- Table setup containing product IDs and functions for handling purchases
local productFunctions = {}
-- ProductId 1138688305 for 
productFunctions[1138688305] = function(receipt, player)
    --we do this because there has to be some benefit in a devproduct.
    local stats = player:FindFirstChild("leaderstats")
    local gold = stats and stats:FindFirstChild("Gold")
    if gold then
        gold.Value = gold.Value + 1
        -- Indicate a successful purchase
        return true
    end
end
 --------------------------------------------------------------------------------------------------------------------------
--DO NOT TOUCH THIS SCRIPT FROM NOW ON OR ELSE YOU WILL NOT GET ROBUX!!!
-- The core 'ProcessReceipt' callback function
local function processReceipt(receiptInfo)

    -- Determine if the product was already granted by checking the data store  
    local playerProductKey = receiptInfo.PlayerId .. "_" .. receiptInfo.PurchaseId
    local purchased = false
    local success, errorMessage = pcall(function()
        purchased = purchaseHistoryStore:GetAsync(playerProductKey)
    end)
    -- If purchase was recorded, the product was already granted
    if success and purchased then
        return Enum.ProductPurchaseDecision.PurchaseGranted
    elseif not success then
        error("Data store error:" .. errorMessage)
    end

    -- Find the player who made the purchase in the server
    local player = Players:GetPlayerByUserId(receiptInfo.PlayerId)
    if not player then
        -- The player probably left the game
        -- If they come back, the callback will be called again
        return Enum.ProductPurchaseDecision.NotProcessedYet
    end

    -- Look up handler function from 'productFunctions' table above
    local handler = productFunctions[receiptInfo.ProductId]

    -- Call the handler function and catch any errors
    local success, result = pcall(handler, receiptInfo, player)
    if not success or not result then
        warn("Error occurred while processing a product purchase")
        print("\nProductId:", receiptInfo.ProductId)
        print("\nPlayer:", player)
        return Enum.ProductPurchaseDecision.NotProcessedYet
    end

    -- Record transaction in data store so it isn't granted again
    local success, errorMessage = pcall(function()
        purchaseHistoryStore:SetAsync(playerProductKey, true)
    end)
    if not success then
        error("Cannot save purchase data: " .. errorMessage)
    end

    -- IMPORTANT: Tell Roblox that the game successfully handled the purchase
    return Enum.ProductPurchaseDecision.PurchaseGranted
end

-- Set the callback; this can only be done once by one script on the server! 
MarketplaceService.ProcessReceipt = processReceipt

note: roblox does not handle these devproduct purchases, so you must NOT alter the core script. you do not need the above script for a gamepass.