Datastore cannot save other players stats why?

I'm trying to learn some datastore of the roblox wiki but when i wrote the code they had and tried to understand it it worked fine for me. But when why friends joins the server i get an error and i get the message the pcall got me.

Why is this happening, why is it working for the datastore to save the stats for me but not my friends or any other players?

Dictionary cannot be stored in DataStore

DataStore could not be accessed! Data might not save.

Script:

local module = {}

local ToolModule = require(game.ReplicatedStorage.Classes.Modules.Tools)

local DataStoreService = game:GetService("DataStoreService")
local playerData = DataStoreService:GetDataStore("PlayerData7")

local AUTOSAVE_INTERVAL = 30

local DATASTORE_RETRIES = 3

local PlayerData = {}

function module:ChangeStat(player, statName, changeValue)
    PlayerData[player][statName] = changeValue
end

function module:AddValue(player, statName, changeValue)
    PlayerData[player][statName] = PlayerData[player][statName] + changeValue
end

function module:ChangeTable(player, statName, item, changeValue)
    PlayerData[player][statName][1][item] = changeValue
end

function module:ReturnStats(player)
    return PlayerData
end

local function DataStoreRetry(DataStoreFunction)
    local tries = 0
    local success = true
    local data = nil
    repeat
        tries = tries + 1
        success, message = pcall(function() data = DataStoreFunction() end)
        print(data)
        if not success then wait(1) end
    until tries == DATASTORE_RETRIES or success
    if not success then
        print(message)
        error("DataStore could not be accessed! Data might not save.")
    end
    return success, data
end

function module:GetStats(player)
    return DataStoreRetry(function()
        return playerData:GetAsync(player.UserId)
    end)
end

local function savePlayerData(player)
    if PlayerData[player] then
        return DataStoreRetry(function()
            return playerData:SetAsync(player.UserId, PlayerData[player])
        end)
    end
end

function LoadData(player)
    return DataStoreRetry(function()
        return playerData:GetAsync(player.UserId)
    end)
end

function SetupPlayerData(player)        
    local success, data = LoadData(player)
    if not success then
        PlayerData[player] = false
    else
        if not data then
            print("Save not found, creating a new save!")
            PlayerData[player] = {
                Cash = 0,
                Level = 1,
                Experience = 0,
                Rebirth = 0,
                Rank = "Beginner",
                Tool = "GravityGun",
                Backpack = "Backpack1",
                BackpackAmount = 0,
                ToolStats = {
                    ToolModule,
                }
            }
            savePlayerData(player)
        else
            PlayerData[player] = data
        end
    end
end

function AutoSave()
    while wait(AUTOSAVE_INTERVAL) do
        for player, data in pairs(PlayerData) do
            print("Saving Data!")
            savePlayerData(player)
        end
    end
end

spawn(AutoSave)

game.Players.PlayerAdded:Connect(SetupPlayerData)

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

    PlayerData[player] = nil
end)

return module