Humanoid is not a valid member of Model? anyone know how to fix this?

I'm scripting from a youtube tutorial and I'm making a tower defense game and for some reason I have a error "Humanoid is not a valid member of model Workspace.Towers.Slinger? (also the error is on line 63)

(towers is my folder where I put my towers in and slinger is the towers name) does anyone know how to fix?

https://youtu.be/wy-Z-xBYbes
that is the youtube video I used for the script and the error is on

local y = result.Position.Y + towerToSpawn.Humanoid.HipHeight + (towerToSpawn.PrimaryPart.Size.Y / 2) is the error

local ReplicatedStorage = game:GetService("ReplicatedStorage")
local RunService = game:GetService("RunService")
local UserInputService = game:GetService("UserInputService")

local towers = ReplicatedStorage:WaitForChild("Towers")

local camera = workspace.CurrentCamera
local gui = script.Parent

local towerToSpawn = nil
local function MouseRaycast(blacklist)
    local mousePosition = UserInputService:GetMouseLocation()
    local mouseRay = camera:ViewportPointToRay(mousePosition.X, mousePosition.Y)
    local raycastParams = RaycastParams.new()

    raycastParams.FilterType = Enum.RaycastFilterType.Blacklist
    raycastParams.FilterDescendantsInstances = blacklist

local raycastResult = workspace:Raycast(mouseRay.Origin, mouseRay.Direction * 1000, raycastParams)


    return raycastResult
end


local function AddPlaceholderTower(name)

    local towerExists = towers:FindFirstChild(name)
    if towerExists then
        towerToSpawn = towerExists:Clone()
        towerToSpawn.Parent = workspace.Towers
    end
end

gui.Spawn.Activated:Connect(function()
    AddPlaceholderTower("Slinger")
end)

UserInputService.InputBegan:Connect(function(input, processed)
    if processed then
        return
    end

    if input.UserInputType == Enum.UserInputType.MouseButton1 then

    end
end)

RunService.RenderStepped:Connect(function()
    if towerToSpawn then
        local result =MouseRaycast({towerToSpawn})
        if result and result.Instance then
            local x = result.Position.X
            local y = result.Position.Y + towerToSpawn.Humanoid.HipHeight + (towerToSpawn.PrimaryPart.Size.Y / 2)
            local z = result.Position.Z

            local cframe = CFrame.new(x,y,z)
            towerToSpawn:SetPrimaryPartCFrame(cframe)
        end
    end
end)