(data saving) string expected got nil?data store wont save my string value

i think im using the data store wrong

local DSService = game:GetService("DataStoreService"):GetDataStore("Level")
game.Players.PlayerAdded:connect(function(plr)
	local Ukey = "id-"..plr.UserId
	local leaderstat = Instance.new("IntValue",plr)
	leaderstat.Name = "leaderstats"
	local LevelValue = Instance.new("IntValue",leaderstat)
	LevelValue.Parent = leaderstat
	LevelValue.Name = "Level"
	local Sp = Instance.new("StringValue",leaderstat)
	Sp.Parent = leaderstat
	Sp.Name = "Power"
	Sp.Value = ""
	local GetSaved = DSService:GetAsync(Ukey)
	if GetSaved then
	LevelValue.Value = GetSaved[1]
	Sp.Value = GetSaved[2]
	else
	local NumbersForSaving = {LevelValue.Value,Sp.Value}
	DSService:SetAsync(Ukey,NumbersForSaving)
	end
end)

game.Players.PlayerRemoving:connect(function(plr)
	local Ukey = "id-"..plr.UserId
	local Savetable = {plr.leaderstats.Level.Value,plr.leaderstats.Sp.Value}
	DSService:SetAsync(Ukey,Savetable)
end)

First off, you are attempting to save two values to the same key. This won't work, as one will overwrite the other. Second, a better way might be to use a dictionary table, in case you have lots of values and it takes a while to find them all. This code should theoretically work.

local DSService = game:GetService("DataStoreService"):GetDataStore("Level")
game.Players.PlayerAdded:connect(function(plr)
    local Ukey = "id-"..plr.UserId
    local leaderstat = Instance.new("IntValue",plr)
    leaderstat.Name = "leaderstats"
    local LevelValue = Instance.new("IntValue")
    LevelValue.Parent = leaderstat
    LevelValue.Name = "Level"
    local Sp = Instance.new("StringValue") ------ this part
    Sp.Parent = leaderstat
    Sp.Name = "Power" ------- until this part
    local GetSaved = DSService:GetAsync(Ukey)
    if GetSaved then
        LevelValue.Value = GetSaved.lvl
        Sp.Value = GetSaved.pwr ----think the problem lies here
    else
        local svtbl = {lvl = LevelValue.Value, pwr = Sp.Value}
        DSService:SetAsync(Ukey,svtb1)
    end
end)


    
game.Players.PlayerRemoving:connect(function(plr)
    local Ukey = "id-"..plr.UserId
    local Savetable = {lvl = plr.leaderstats.Level.Value, pwr = plr.leaderstats.Sp.Value}
    DSService:SetAsync(Ukey,Savetable)
end)

Try storing all your values in one table, rather than 2. Try this:

local DSService = game:GetService("DataStoreService"):GetDataStore("Level")
game.Players.PlayerAdded:connect(function(plr)
    local Ukey = "id-"..plr.UserId
    local leaderstat = Instance.new("IntValue",plr)
    leaderstat.Name = "leaderstats"
    local LevelValue = Instance.new("IntValue")
    LevelValue.Parent = leaderstat
    LevelValue.Name = "Level"
    local Sp = Instance.new("StringValue") ------ this part
    Sp.Parent = leaderstat
    Sp.Name = "Power" ------- until this part
    local GetSaved = DSService:GetAsync(Ukey)
    if GetSaved then
    LevelValue.Value = GetSaved[1]
    Sp.Value = GetSaved[2] ----think the problem lies here
    else
    local NumbersForSaving = {LevelValue.Value,Sp.Value}
    DSService:SetAsync(Ukey,NumbersForSaving)
    end
end)

game.Players.PlayerRemoving:connect(function(plr)
    local Ukey = "id-"..plr.UserId
    local Savetable = {plr.leaderstats.Level.Value,plr.leaderstats.Sp.Value}
    DSService:SetAsync(Ukey,Savetable)
end)

I also recommend that you save the player's data occasionally because sometimes servers shut down randomly and can cause data loss.