Can't access PlayerGui in ServerScript when a purchase is completed - roblox

Question

So, I want to make if a Player succesfully donate in my game, an GUi will show up in the Player screen with a Tween Animation that says Purchase is completed
When I tested it out, I expected when I trying to test to purchase donate, it will show up a GUi, But, the actual results is already showed up in Output. When I tried to playtest it, An error ServerScriptService.Purchases:14: attempt to index nil with 'WaitForChild' showed up in Output
I already searched on Google and still can't understand.
Here's the code:
-- Products for purchases
local Donate1ProductID = 1296480045
local Donate2ProductID = 1296484976
local Donate3ProductID = 1296484935
local Donate4ProductID = 1296484932
local Donate5ProductID = 1296483595
local Donate6ProductID = 1296484931
local Donate7ProductID = 1296484933
-- Required depencies/services
local MarketplaceService = game:GetService("MarketplaceService")
local Players = game:GetService("Players")
local LocalPlayer = Players.LocalPlayer
local Main = LocalPlayer:WaitForChild("PlayerGui"):WaitForChild("AntiPiracyCheck")
-- Code
MarketplaceService.ProcessReceipt = function(receiptInfo)
local player = Players:GetPlayerByUserId(receiptInfo.PlayerId)
if receiptInfo.ProductId == Donate1ProductID or Donate2ProductID or Donate3ProductID or Donate4ProductID or Donate5ProductID or Donate6ProductID or Donate7ProductID then
Main.PurchaseSuccess:TweenPosition(
UDim2.new(0.258, 0,0.279, 0),
Enum.EasingDirection.InOut,
Enum.EasingStyle.Quad,
1,
true
)
return Enum.ProductPurchaseDecision.PurchaseGranted
end
end

Answer 1

Because it's a server script LocalPlayer doesn't exist therefore it's a nil value.
-- Products for purchases
local Donate1ProductID = 1296480045
local Donate2ProductID = 1296484976
local Donate3ProductID = 1296484935
local Donate4ProductID = 1296484932
local Donate5ProductID = 1296483595
local Donate6ProductID = 1296484931
local Donate7ProductID = 1296484933
-- Required depencies/services
local MarketplaceService = game:GetService("MarketplaceService")
local Players = game:GetService("Players")
-- Code
game.Players.PlayerAdded:Connect(function(LocalPlayer)
MarketplaceService.ProcessReceipt = function(receiptInfo)
local player = Players:GetPlayerByUserId(receiptInfo.PlayerId)
local Main = player:WaitForChild("PlayerGui"):WaitForChild("AntiPiracyCheck")
if receiptInfo.ProductId == Donate1ProductID or Donate2ProductID or Donate3ProductID or Donate4ProductID or Donate5ProductID or Donate6ProductID or Donate7ProductID then
Main.PurchaseSuccess:TweenPosition(
UDim2.new(0.258, 0,0.279, 0),
Enum.EasingDirection.InOut,
Enum.EasingStyle.Quad,
1,
true
)
return Enum.ProductPurchaseDecision.PurchaseGranted
end
end