Modified Roblox's Default ProcessReceipt Callback Code

-- Table setup containing product IDs and functions for handling purchases
local ProductFunctions = {}

local Settings = {
    Duration = 10,
    GrowScale = 1,
    TweenDuration = .75,
    ShrinkScale = 0,

    NotProcessedYet = Enum.ProductPurchaseDecision.NotProcessedYet,
    PurchaseGranted = Enum.ProductPurchaseDecision.PurchaseGranted,

    PurchaseHistoryDataStoreKey = "PurchaseHistory", -- PurchaseHistoryDataStoreName
}

local MarketplaceService = game:GetService("MarketplaceService")
local TweenService = game:GetService("TweenService")
local DataStoreService = game:GetService("DataStoreService")
local Players = game:GetService("Players")
local ReplicatedStorage = game:GetService("ReplicatedStorage")
local Modules = ReplicatedStorage:WaitForChild("Modules")
local ProductIDS = require(Modules:WaitForChild("ProductIDS"))

-- MODULE SCRIPT CODE
--[[
    local ProductIDS = {}

    ProductIDS.TestID = 1817343951

    return ProductIDS
]]

-- Data store for tracking purchases that were successfully processed
local PurchaseHistoryDataStore = DataStoreService:GetDataStore(Settings.PurchaseHistoryDataStoreKey)
local TweenPlayerInfo = TweenInfo.new(Settings.TweenDuration)

-- ProductId ProductIDS.TestID For a full Shrink Toggles
ProductFunctions[ProductIDS.TestID] = function(Receipt, Player : (Player))
    -- Logic/code for player buying a full toggle shink/grow (may vary)
    local Character = Player.Character or Player.CharacterAdded:Wait()
    local Humanoid = Character:FindFirstChild("Humanoid")
    if Character and Humanoid and Humanoid ~= nil then
        -- Shrinks The Player to stick man
        TweenService:Create(Humanoid.BodyTypeScale, TweenPlayerInfo, {Value = Settings.ShrinkScale}):Play()
        TweenService:Create(Humanoid.BodyWidthScale, TweenPlayerInfo, {Value = Settings.ShrinkScale}):Play()
        TweenService:Create(Humanoid.HeadScale, TweenPlayerInfo, {Value = Settings.ShrinkScale}):Play()
        task.delay(Settings.Duration, function()
            TweenService:Create(Humanoid.BodyTypeScale, TweenPlayerInfo, {Value = Settings.GrowScale}):Play()
            TweenService:Create(Humanoid.BodyWidthScale, TweenPlayerInfo, {Value = Settings.GrowScale}):Play()
            TweenService:Create(Humanoid.HeadScale, TweenPlayerInfo, {Value = Settings.GrowScale}):Play()
        end)
    end
    -- Indicate a successful purchase
    return true
end

-- The core 'ProcessReceipt' callback function
local ProcessReceipt = function(ReceiptInfo)
    -- Determine if the product was already granted by checking the data store
    local PlayerProductKey = ReceiptInfo.PlayerId .. "_" .. ReceiptInfo.PurchaseId
    local Success, Result, ErrorMessage, IsPurchaseRecorded

    local Purchased = false

    Success, ErrorMessage = pcall(function()
        Purchased = PurchaseHistoryDataStore:GetAsync(PlayerProductKey)
    end)

    -- If purchase was recorded, the product was already granted
    if Success and Purchased then
        return Settings.PurchaseGranted
    elseif not Success then
        error("Data store error:" .. ErrorMessage)
    end

    -- Determine if the product was already granted by checking the data store
    Success, IsPurchaseRecorded = pcall(function()
        return PurchaseHistoryDataStore:UpdateAsync(PlayerProductKey, function(AlreadyPurchased)
            if AlreadyPurchased then
                return true
            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 nil
            end

            local Handler = ProductFunctions[ReceiptInfo.ProductId]

            local Success, Result = pcall(Handler, ReceiptInfo, Player)

            if not Success or not Result then
                -- If granting the product failed, do NOT record the purchase in datastores.
                error("Failed to process a product purchase for ProductId: " .. tostring(ReceiptInfo.ProductId) .. " Player: " .. tostring(Player) .. " Error: " .. tostring(Result))
                return nil
            end

            -- Record the transcation in purchaseHistoryStore.
            return true
        end)
    end)

    if not Success then
        error("Failed to process receipt due to data store error.")
        return Settings.NotProcessedYet
    elseif IsPurchaseRecorded == nil then
        -- Didn't update the value in data store.
        return Settings.NotProcessedYet
    else
        -- IMPORTANT: Tell Roblox that the game successfully handled the purchase
        return Settings.PurchaseGranted
    end
end

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