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