Datastore not saving data or giving error?

Try this

-- Adding variables like the data store service, myData store is your data store, Players left is to detect if there's amount of players to detect when the server can shutdown
local dataStoreService = game:GetService("DataStoreService")
local myDataStore = dataStoreService:GetDataStore("RobloxDataStore")
local playersLeft = 0

game.Players.PlayerAdded:Connect(function(player)

    -- Everytime a player joins it add 1 more to players left

    playersLeft = playersLeft + 1

    -- Adding money to the play
    local leaderstats = Instance.new("Folder")
    leaderstats.Name = "leaderstats"
    leaderstats.Parent = player

    local money = Instance.new("IntValue")
    money.Name = "Money"
    money.Value = 0
    money.Parent = leaderstats

    -- This adds data into the player data with userid

    local PlayerUserId = player.UserId

    -- Making a blank variable to store data

    local player_data

    -- Checks if its successfull or else you get an error message
    -- Makes a pcall so if theres an error it won't break the script

    local success, errorMessage = pcall(function()

        -- Sets player_data as players userid in your data store

        player_data = myDataStore:GetAsync(PlayerUserId)
    end)

    -- If its successfull then the money will be what we saved

    if success then
        money.Value = player_data.Money
    end
end)

-- Makes a bindable event, Used to tell the script to do something when the game is shutting down

local bindableEvent = Instance.new("BindableEvent")

-- Fires what a player leaves the game

game.Players.PlayerRemoving:Connect(function(player)

    -- Gets the userid again

    local playerUserId = player.UserId

    -- The player_data you can save money is your money value

    local player_data = {
        Money = player.leaderstats.Money.Value
    }

    -- When a player leaves it will set your money to money in player data at amount of money you have

    local success, errorMessage = pcall(function()
        myDataStore:SetAsync(playerUserId, player_data)

        -- Removes from players left

        playersLeft = playersLeft - 1

        -- Fires the bindable event

        bindableEvent:Fire()
    end)

    -- If it was successfull then it prints saved to tell you that it was successfull else it tell you what the problem is

    if success then
        print("Saved!")
    else
        warn(errorMessage)
    end
end)

-- If the players left is above 0 then the server is gonna wait until everyones data was saved and then it can shut down

if playersLeft > 0 then
    bindableEvent.Event:Wait()
end

To add more leader stats add this under money

    local coins = Instance.new("IntValue")
    coins.Name = "Coins"
    coins.Value = 0
    coins.Parent = leaderstats

To load it add this to the success in players added

coins.Value = player_data.Coins

To save it add this in the player_data table in playerRemoving

Coins = player.leaderstats.Coins.Value