My event wont fire in my Health Bar code and there are no errors, what's wrong with this code?

Hi, I'm trying to create a healthbar that detects when the player takes damage on the server, and changes the UI on the client. Here is my code. I get no errors, and nothing happens.

Serverscript in serverscriptservice:

local players = game("GetService", "Players")
local replicatedStorage = game("GetService", "ReplicatedStorage")
local events = replicatedStorage.Events
local event = events.HealthEvent
players.PlayerAdded:connect(function(player)
	print(player.ClassName)
	local gui = player:WaitForChild("Backpack")
	print(gui)
	local scriptOne = gui:WaitForChild('HealthHandler')
	player.CharacterAdded:connect(function(character)
		character.Humanoid.HealthChanged:connect(function(player)
			event:FireClient(player)
			end)
	end)
end)

Local script in StarterPack

local players = game("GetService", "Players")
local replicatedStorage = game("GetService", "ReplicatedStorage")
local events = replicatedStorage.Events
local event = events.HealthEvent
local player = players.LocalPlayer
event.OnClientEvent:Connect(function()
	print("hi")
	player.CharacterAdded:connect(function(character)
		print(character)
		local health = character.Humanoid.Health/100
		player.PlayerGui.HealthUI.HealthFrame.Healthbar.Size = UDim2.new(health,0,1,0)
	end)
end)

I believe that the issue is that you wait on the Player's Character to spawn twice; your server side function waits for a Character to be added, and the event you call does the same. Since you aren't adding the Character twice, the function (client side) never runs.

Also notable is that running a server side handler for Player health seems ridiculous.

In a LocalScript (now tested and working):

local player = game.Players.LocalPlayer;
local gui = player.PlayerGui:WaitForChild("HealthUI").HealthFrame.Healthbar;

local c = player.Character;
c.Humanoid.HealthChanged:connect(function(newhealth)
	gui.Size = UDim2.new(newhealth/c.Humanoid.MaxHealth, 0, 1, 0);
end)