[STILL UNANSERWED] Buying in game currency script help?

local productId = 20983086 
local player = game.Players.LocalPlayer

script.Parent.MouseButton1Click:connect(function() 
    Game:GetService("MarketplaceService"):PromptProductPurchase(player, productId)
end)




if plr and plr:FindFirstChild"leaderstats" and plr.leaderstats:FindFirstChild"Credits" then
plr.leaderstats.Credits.Value = plr.leaderstats.Credits.Value + script.Parent.Name 
end

Hey, so i have this code, were the player buy '50 credits' which i have as a developer product it opens up okay but when bought, it doesn't give the player the sed amount they bought and i don't know how to change the script to make it happen.

I don't know if you'll need it but this is the leader board, which is also working properly

function onPlayerEntered(newPlayer) 

    local stats = Instance.new("IntValue") 
    stats.Name = "leaderstats"

    local robux = Instance.new("IntValue") 
    robux.Name = "Credits"
    robux.Value = 0                         
    robux.Parent = stats 
        stats.Parent = newPlayer 
end 
game.Players.ChildAdded:connect(onPlayerEntered)