I made this script that it should level up, but it doesn't seem to?

When I check the error it says ServerScriptService.LevelUp:2: attempt to index nil with 'FindFirstChild' If anyone can help me I would be gratefull here's the script

local plr = game.Players.LocalPlayer
local Stats = game.Players.LocalPlayer:FindFirstChild("Stats") --This is finds the Stats
local XP = Stats:FindFirstChild("XP") -- This should find XP
if XP.Value > 70 *plr.leaderstats.Level.Value then -- I wanted to do if the XP is higher then 70 times level so what I went times by level is when you get lvl 2 it times it to 140
	plr.leaderstats.Level.Value = plr.leaderstats.Level.Value +1 -- this gives it
end

Hope I explained it right to you guys Anyone can help thanks again

I think your problem is with line 3 it's trying to find the child "XP" when it does not exist as you did not create it with Instance and same for the stats

I would remove the stats stuff you made manually and create it with Instance by checking when a player joins the game with a server script in ServerScriptService

Example:

game.Players.PlayerAdded:Connect(function(plr) -- You can change plr to anything as its just a 		local value
local stats = Instance.new("Folder") -- The object you make with instance can be changed
stats.Name = "leaderstats" -- If the name is not leaderstats it will not show on the leaderboard but thats your choice
stats.Parent = plr

local lv = Instance.new("IntValue") 
lv.Name = "Level" -- Name string can be change
lv.Parent = stats

local maxxp = Instance.new("IntValue") 
maxxp.Name = "Max XP" -- Name string can be change
maxxp.Parent = plr

local xp = Instance.new("IntValue") 
xp.Name = "XP" -- Name string can be change
xp.Parent = stats

while wait() do -- Same thing as while true do but It won't crash your game
if xp.Value >= maxxp.Value then
xp.Value = xp.Value - maxxp.Value -- I fixed up your exp decrease script for ya so it does not default it to 0 instead it removes as much xp is needed to level up!
maxxp.Value = maxxp.Value * 2
lv.Value = lv.Value + 1
end
end
end)

If you want this stuff to be saved I would look at datastore tutorials they are complicated for beginners but still is needed for a rpg game!