Dev Product Buttons Aren't Working?

I'm developing a game where players can buy in-game cash for Robux. I used a model that has SurfaceGui buttons that are supposed to prompt the player to buy a dev product. However, in Studio and in-game pressing the button does not prompt anything.

Here is my code for one of the buttons:

local buyButton = script.Parent
local productId = 567187672 
local mps = game:GetService("MarketplaceService")

function getPlayerById(id)
for i,v in pairs(game.Players:GetPlayers()) do
if v.userId == id then
return v
end
end
end

buyButton.MouseButton1Down:connect(function()
mps:PromptProductPurchase(game.Players.LocalPlayer, productId)
end)

mps.ProcessReceipt = function(info)
local plr = getPlayerById(info.PlayerId)
if plr and plr:FindFirstChild("leaderstats") and plr.leaderstats:FindFirstChild("Cash") then
plr.leaderstats.Cash.Value = plr.leaderstats.Cash.Value + 1000
end
end