(Still Unanswered) How to fix this? i'm making custom overhead health GUI

The Code In StarterCharacterScript -

local char = script.Parent
char.Changed:connect(function()
	print("ads")
	local hum = char.Humanoid
	local health = hum.Health
	local maxHealth = hum.MaxHealth
	char.Head.HealthBar.GreenBar.Size = UDim2.new(health/maxHealth,0,1,0)
end)

Also the Billboard GUI is in the characters head

Problem -

Whenever the humanoid takes damage the green bar wont scale to its health.

Also its a billboard GUI in the players head

If I am correct, char is referencing the Player's model instead of the humanoid. If you want the healthbar to update when the player takes damage, then the function must fire when the humanoid changes (specifically the humanoid's health).

Try using this:

local char = script.Parent
local human = char:FindFirstChild('Humanoid')

human.Changed:connect(function()
	print('test')
	local health = human.Health
	local maxhealth = human.MaxHealth
	char.Head.HealthBar.GreenBar.Size = UDim2.new(health/maxHealth,0,1,0)
end)