whenever i press the key that i have set up in the code nothing happens, why is this ?

I will show the full code, however it is inside a tool if that helps.

local tool = script.Parent
local KOValue = "Kills"
local player = game:GetService("Players").LocalPlayer
local replicatedstorage = game:GetService("ReplicatedStorage")
local remoteFunction = replicatedstorage:WaitForChild("RemoteFunction")
local gungui = tool.Parent.Parent.PlayerGui:WaitForChild("gungui")
local ammo = gungui:WaitForChild("am")
local maxammo = gungui:WaitForChild("maxam")
local fetchBulletsLeft = replicatedstorage:WaitForChild("BulletsLeft")
local UIS = game:GetService("UserInputService")
local re = gungui:WaitForChild("reload")

local Bullet = replicatedstorage:WaitForChild("bullet")
local basepart = game.Workspace.Terrain

local bulletspeed = 500
local damage = 25
local FireRate = 0.1
local out = false
local attack = false

local ko = false

local function touching(hit)
	local zom = hit.Parent.Name == "zombie"
	if zom then
		local zombie =hit.Parent.Zombie
		wait()
		if zombie.Health <= 0 and ko == false then
			ko = true
			local pla = game.Players:GetPlayerFromCharacter(tool.Parent)
			pla.leaderstats[KOValue].Value = pla.leaderstats[KOValue].Value + 1
			wait(0.1)
			ko = false
		end
	end
end	

tool.Activated:Connect(function(hit)

	if out == false then 
		if attack == false then 
			attack = true

			local player = game.Players:GetPlayerFromCharacter(tool.Parent)
			local MouseHitLookVector = remoteFunction:InvokeClient(player)

			local NewBullet = Bullet:Clone()
			NewBullet.CFrame = tool.Handle.CFrame
			NewBullet.Parent = game.Workspace
			
			NewBullet.Velocity = MouseHitLookVector * bulletspeed
			NewBullet.Touched:Connect(touching)
			if ammo.Value > 0 then
				ammo.Value -= 1
				gungui.Currentammo.Visible = true
				gungui.ammo.Visible = true
			elseif maxammo.Value == 0 and ammo.Value == 0 then
				out = true
			else
				re.Visible =true	
				out = true
				gungui.Currentammo.Visible = false
				gungui.ammo.Visible = false
			end
			
			
			wait(FireRate)
			attack = false
			basepart.Touched:Connect(function(lit)
				if lit.Name == "bullet" then
					wait(2)
					lit:Destroy()
				end
					
			end)


		end
	else
		UIS.InputBegan:Connect(function(key)
			print("fuck my life")
			if key == Enum.KeyCode.R then
				if re.Visible == true then
					re.Visible = false
					wait(2)
					ammo.Value = 25
					maxammo.Value -= 25
					out = false
				end
			end
		end)	
	end
end)

thankyou for reading, i hope i can fix this :)

See documentation for InputBegan, it returns InputObject, not Enum.KeyCode, you need to replace line 83 with this:

if key.KeyCode == Enum.KeyCode.R then

Though your script still has major issue, everytime Activated fires and out is true you are creating a new connection with :Connect, thus if you activate the tool 20 times with out being true, you are going to have 20 new connections and all of them will be active, this is bad for performance and memory, fix that by creating only a single connection and check if out (or other variable you might need) is true / false inside of it. You have done same mistake with basepart.Touched, though idk what exactly you wanted to achieve with it so I will leave it up to you to fix. Here is an example of what I mean:

UIS.InputBegan:Connect(function(key)
  -- Stop continuing the code if these conditions are not true
  -- you should specify your own conditions, toolIsEquipped
  -- variable does not even exist, just a placeholder
  if not toolIsEquipped or not out then
    return
  end
  
  print("fuck my life")
  if key.KeyCode == Enum.KeyCode.R then
    if re.Visible == true then
      re.Visible = false
      wait(2)
      ammo.Value = 25
      maxammo.Value -= 25
      out = false
    end
  end
end)    

Whenever you get better, you can try other method by disconnecting and connecting events.

thankyou for your help, i ended up fixing it just by using a remote function to grab players data, due to the script being a server script.