How to make character heal using animation and keydown function?

Hello everyone, I am new to scripting, and I was looking for some help of this potion animation I was doing.

Basically, I created a Local Script where if your health is below 50, you can press a certain key which will play an animation, and restore health. For some reason, it's not working, so I was looking for some help.

Local Script:

local player = game.Players.LocalPlayer
local mouse = player:GetMouse()
local animation = Instance.new("Animation")
animation.AnimationId = "http://www.roblox.com/Asset?ID=734045225"
local humanoid = character:FindFirstChild('Humanoid')
local HealthGain = 20
	

if humanoid then
	local currentHealth = humanoid.Health
	local newHealth = currentHealth + HealthGain
	humanoid.Health = newHealth
end

if player.Character.Humanoid.Health < 50 then
mouse.KeyDown:connect(function(key)
	if key == "h" then 
        animation.Play()
		wait (5)
		animation.Stop()
        
if humanoid then
local currentHealth = humanoid.Health
local newHealth = currentHealth + HealthGain
humanoid.Health = newHealth

end		
		
	end
	
end`)

I can't quite figure out the problem with my script, but I have a feeling it has something to do with the keydown function, or the animation functions.

I'm quite new to scripting, so much help is appreciated!

Line 05, you didn't define what character was. The answer is on Line 03.

local player = game.Players.LocalPlayer
local mouse = player:GetMouse()
local character = player.Character
local animation = Instance.new("Animation")
animation.AnimationId = "http://www.roblox.com/Asset?ID=734045225"
local humanoid = character:FindFirstChild('Humanoid')
local HealthGain = 20


if humanoid then
    local currentHealth = humanoid.Health
    local newHealth = currentHealth + HealthGain
    humanoid.Health = newHealth
end

if player.Character.Humanoid.Health < 50 then
mouse.KeyDown:connect(function(key)
    if key == "h" then 
        animation.Play()
        wait (5)
        animation.Stop()

if humanoid then
local currentHealth = humanoid.Health
local newHealth = currentHealth + HealthGain
humanoid.Health = newHealth

end     

    end

end`)