Tween Position Won't Change?

I have a script I'm trying to write where, upon clicking an ImageScript the script is a child of, the image button will move a frame under the same screen GUI up on to the screen/down off the screen. However whenever I run it the goal position stays the same, even though I changed the value. Here's the script:

local ShopGui = script.Parent.Parent
local Shop = ShopGui.Shop
local Players = game.Players
local Teams = game.Teams

local START_POSITION = UDim2.new(0.2, 0, 1.2, 0)
local GOAL_POSITION = UDim2.new(0.2, 0, 0.2, 0)

local guiObject = Shop

local function callback(state)
    if state == Enum.TweenStatus.Completed then
    elseif state == Enum.TweenStatus.Canceled then
    end
end
local endpos = Instance.new("BoolValue")

function onMouseClick()
    if  Shop.Visible == true then
        print("turning off")
        local START_POSITION = UDim2.new(0.2, 0, 0.2, 0)
        local GOAL_POSITION = UDim2.new(0.2, 0, 1.2, 0)
        endpos.Value = false
    else
        local START_POSITION = UDim2.new(0.2, 0, 1.2, 0)
        local GOAL_POSITION = UDim2.new(0.2, 0, 0.2, 0)
        endpos.Value = true
    end
    print (GOAL_POSITION)
    Shop.Visible = true
    Shop.Active = true
    guiObject.Position = START_POSITION
    local willPlay = guiObject:TweenPosition(
        GOAL_POSITION,           -- Final position the tween should reach
        Enum.EasingDirection.In, -- Direction of the easing
        Enum.EasingStyle.Sine,   -- Kind of easing to apply
        0.5,                       -- Duration of the tween in seconds
        true,                    -- Whether in-progress tweens are interrupted
        callback                 -- Function to be callled when on completion/cancelation
    )
    wait(2)
    Shop.Visible = endpos.Value
    Shop.Active = endpos.Value
    print (endpos.Value)
end

script.Parent.MouseButton1Down:connect(onMouseClick)

Really sorry, I'm sure this is just a rookie mistake. Thanks for any feedback!