Yes, I do have API access enabled.
local DSS = game:GetService("DataStoreService")
local leveldatastore = DSS:GetDataStore("LevelNumber")
game.Players.PlayerAdded:connect(function(player)
local level = Instance.new("NumberValue",player)
level.Name = "level"
level.Value = leveldatastore:GetAsync(player.UserId) or 1
leveldatastore:SetAsync(player.UserId,level.Value)
end)

2 comments
For future reference with datastores, I recormend https://scriptinghelpers.org/questions/25774
Please explain your code, where he went wrong, and what you did to fix it.