I am making an obby checkpoint system with saves and am running into the following issue

Stage is not a valid member of Folder

here are my code snippets: script in checkpoint part

	if humanoid then
		print(plr.Parent.Name)
		local player1 = game:GetService("Players"):GetPlayerFromCharacter(workspace[plr.Parent.Name])
		print(type(player1))
		local spawns = datastoreservice:GetDataStore("spawns")
		print(player1.userId)
		spawns:SetAsync(player1.userId, encodeCFrame(player1.Character:WaitForChild("HumanoidRootPart").CFrame))
--		printTable(player1.leaderstats:GetChildren())
		game:GetService("Players")[player1.Name].leaderstats["Stage"] = script.Parent.Name
		
	end
end)

script in serverscriptservice

game:GetService('Players').PlayerAdded:Connect(function(player)
	local leaderstats = Instance.new("Folder")
	leaderstats.Name = "leaderstats"
	leaderstats.Parent = player
	
	local level = Instance.new("IntValue", leaderstats)
	
	level.Name = "Stage"
	level.Value = 1
	print(player.leaderstats.Stage)

Please could someone help as to why this error is being caused as i can see the playername.leaderstats.Stage value in explorer but in the script it cant find it any help would be appreciated Josh Edit: fix code edit 2: only include references to leaderstats

You forgot the WaitForChild incase the instance isn't yet created / loaded in yet. Also try Stage.Value?

-- >> Checkpoint Script
local datastoreservice = game:GetService("DataStoreService")
local spawns = datastoreservice:GetDataStore("spawns")

script.Parent.Touched:Connect(function(hit)
    local humanoid = hit.Parent:FindFirstChildWhichIsA("Humanoid")

    if humanoid then
        local player1 = game.Players:GetPlayerFromCharacter(hit.Parent)
        spawns:SetAsync(player1.userId, encodeCFrame(player1.Character:WaitForChild("HumanoidRootPart").CFrame))
--      printTable(player1.leaderstats:GetChildren())
        player1.leaderstats:WaitForChild("Stage") = script.Parent.Name
    end
end)

Stage is not a property.

I found the issue. It's this:

game:GetService("Players")[player1.Name].leaderstats["Stage"] = script.Parent.Name

You are treating Stage as like a property, however this fails as it's not a property.

Just append a .Value.

Also this code can severely be cleaned.

First off, why go backwards to game:GetService("Players") only to index it for player1.Name?

This could be simplified to

player1.leaderstats.Stage.Value = script.Parent.Name

Mostly I answered because I wanted to clean up your printTable function.

It can be as simple as...

local function print_table(t)
	print(string.format("{%s}", table.concat(t, ", ")))
end

I would clean up your code, however it's too messy and beyond cleaning. You may need to restructure and rewrite parts of your code base to clean it up.