Prompt to buy a gamepass?

AFAIK, the code is well written, without any errors.. Actually, I think I've seen it before, I believe that's in a template. So, first of all, I advice you to check to see if that gamepass ID actually exists, and it is one that you created (5327756).

Assuming you did, you turned the code into a function, but never called it. So:

We can make it run the function:

-- This code should be within a 'LocalScript' object
local MarketplaceService = game:GetService("MarketplaceService")
local Players = game:GetService("Players")

local gamePassID = 5327756  -- Change this to your game pass ID

-- Function to prompt purchase of the game pass
local function promptPurchase()

    local player = Players.LocalPlayer
    local hasPass = false

    local success, message = pcall(function()
        hasPass = MarketplaceService:UserOwnsGamePassAsync(player.UserId, gamePassID)
    end)

    if not success then
        warn("Error while checking if player has pass: " .. tostring(message))
        return
    end

    if hasPass == true then
        -- Player already owns the game pass; tell them somehow
    else
        -- Player does NOT own the game pass; prompt them to purchase
        MarketplaceService:PromptGamePassPurchase(player, gamePassID)
    end
end

-- Run the function
promptPurchase()

or make it actual running code, or by other words, remove the function indication:

-- This code should be within a 'LocalScript' object
local MarketplaceService = game:GetService("MarketplaceService")
local Players = game:GetService("Players")

local gamePassID = 5327756  -- Change this to your game pass ID

-- Make this not be a function, so it will run.
local player = Players.LocalPlayer
local hasPass = false

local success, message = pcall(function()
    hasPass = MarketplaceService:UserOwnsGamePassAsync(player.UserId, gamePassID)
end)

if not success then
    warn("Error while checking if player has pass: " .. tostring(message))
    return
end

if hasPass == true then
    -- Player already owns the game pass; tell them somehow
else
    -- Player does NOT own the game pass; prompt them to purchase
    MarketplaceService:PromptGamePassPurchase(player, gamePassID)
end

If it works, please mark this as the correct answer. :P