Why are these Variables not recognized/nil?

I'm very new to scripting, and I'm trying to create a UI that appears when a proximity prompt is pressed, and which disappears after a few seconds or when the player is 15 studs away, :disconnect()ing the RunService.Heartbeat

The variable "label" defined in line 6 does not print a value when prompted, and does not change when modified by timeLeft

The variable "connection" defined in line 12 gives an error and won't disconnect the Heartbeat: (Fixed)

Workspace.SuppliesContainer.GainSupplies:29: attempt to index nil with 'disconnect' (Fixed)

This is a regular script with the directory Workspace.SuppliesContainer.GainSupplies Everything else in this code appears to work perfectly fine.

local globalVariables = require(game.ReplicatedStorage.GlobalVariables)
local ReplicatedStorage = game.ReplicatedStorage
local RunService = game:GetService("RunService")
local Players = game:GetService("Players")
local suppliesContainer = script.Parent
local label = game.StarterGui.SuppliesGainGUI.SuppliesGainLabel

local function startSuppliesTimer(timeLeft, PlayerTorso, PlayerGui, supplies)

	local delayEvent = Instance.new("BindableEvent")
	local connection
	connection = RunService.Heartbeat:Connect(function(step)
		print(connection)
		print(timeLeft)
		timeLeft -= step
		local seconds = math.floor(timeLeft % 60)
		label.Text = string.format("i", seconds)
		print(label.Text)
		local distance = (suppliesContainer.Position - PlayerTorso.Position).Magnitude
		print(distance)
		if distance > 15 then
			delayEvent:Fire()
			connection:disconnect()
			PlayerGui.SuppliesGainGUI.Enabled = false
		end
		if timeLeft <= 0 then
			delayEvent:Fire()
			connection:disconnect()
			while globalVariables.squareProgress ~= 0 do
				globalVariables.squareProgress = 0
				wait(0.01)
			end
			globalVariables.squareActive = true
			label.Text = "Supplies Gathered!"
			local sound = Instance.new("Sound", game.Workspace)
			sound.SoundId = "rbxassetid://9120129807"
			sound.PlayOnRemove=true
			sound.Volume = 3
			sound:Play()
			if supplies then
				supplies.Value = supplies.Value + 1
			end
			wait(1)
			PlayerGui.SuppliesGainGUI.Enabled = false
		end

	end)

	delayEvent.Event:Wait()
	
end

workspace.SuppliesContainer.ProximityPrompt.Triggered:Connect(function(playerWhoActivated)
	local humanoid = playerWhoActivated.Character:FindFirstChildWhichIsA("Humanoid")
	print(humanoid)
	if humanoid then
		local PlayerGui = playerWhoActivated.PlayerGui
		-- Update the player's leaderboard stat
		local leaderstats = playerWhoActivated.leaderstats
		local supplies = leaderstats and leaderstats:FindFirstChild("Supplies")
		local PlayerTorso = playerWhoActivated.Character.UpperTorso
		print("should start")
		PlayerGui.SuppliesGainGUI.Enabled = true
		startSuppliesTimer(10, PlayerTorso, PlayerGui, supplies)
	end
end)