I can't "Connect" my function it says passed value is not a function when it is why??

Output: Attempt to connect failed: Passed value is not a function

Why is it saying that when it is a function, how can I fix it?

Thanks in advance.

Code:

local button = script.Parent
local Cam = workspace.Camera
local itemcam = workspace:WaitForChild("Shop").Cams.Cam
local player = game.Players.LocalPlayer
local PlayerGui = player:WaitForChild("PlayerGui")
local Input = game:GetService("UserInputService")
---
function OnClick()
        local ScreenGui = Instance.new("ScreenGui",PlayerGui)
        ScreenGui.Name = "Shop_Ui"
        local Frame = Instance.new("Frame",ScreenGui)
        local Buy_Button = Instance.new("TextButton",ScreenGui)
        Frame.Size = UDim2.new(0, 1920,0, 1079)
        Frame.Position = UDim2.new(0, 0,0, 0)
        Frame.BackgroundColor3 = Color3.fromRGB(255, 255, 255)
        Frame.BackgroundTransparency = 1
        Frame.BackgroundColor3 = Color3.fromRGB(255, 229, 124)
        --Fade
        for i = 1,20 do
                Frame.BackgroundTransparency = Frame.BackgroundTransparency -0.05
                wait(0.01)
        end

        repeat wait()
        Cam.CameraType = Enum.CameraType.Scriptable
until Cam.CameraType == Enum.CameraType.Scriptable
        Cam.CFrame = itemcam.CFrame
        wait(0.5)
                for i = 1,20 do
                Frame.BackgroundTransparency = Frame.BackgroundTransparency +0.05
                wait(0.01)
                end
                        local Buy_Button = Instance.new("TextButton",ScreenGui)
                        Buy_Button.Name = "Buy_Button"
                        Buy_Button.Font = Enum.Font.Cartoon
                        Buy_Button.TextScaled = true
                        Buy_Button.Text = "Buy"
                        Buy_Button.BorderSizePixel = 3
                        Buy_Button.BorderColor3 = Color3.fromRGB(255,255,255)

                        if Input.TouchEnabled == true then --Player On Phone
                                Buy_Button.Size = UDim2.new(0, 78,0, 30)
                                Buy_Button.Position = UDim2.new(0.43, 0,0.841, 0)
                        elseif Input.KeyboardEnabled == true then
                                Buy_Button.Size = UDim2.new(0, 189,0, 65)
                                Buy_Button.Position = UDim2.new(0.5, 0,0.895, 0)

 function OnHover()
        button.ImageColor3 = Color3.fromRGB(255, 222, 121)
        for i = 1,5 do
                button.Rotation = button.Rotation +2
                wait(0.01)
        end

                for i = 1,5 do
                button.Rotation = button.Rotation -2
                wait(0.01)
                end
                                for i = 1,5 do
                button.Rotation = button.Rotation +2
                wait(0.01)
                                end
                                                                for i = 1,5 do
                button.Rotation = button.Rotation -2
                wait(0.01)
                button.ImageColor3 = Color3.fromRGB(255, 255, 255)
             end
end
end
end
button.MouseEnter:Connect(OnHover)
button.Activated:Connect(OnClick)