Why is the script not detecting the value change?

I have an upgrade script. The 1st cost is 17. I can buy it for 17 but I can keep buying it for 17, yet the cost value is actually raising and more than 17. How come the script isn't detecting the value change?

upgrade script:

UpgradeBackpack.OnServerInvoke = function(player)
    local cost = player.UpgradeCosts.BackpackUpgrade
    if cost.Value <= player.leaderstats["Coins"].Value then
            player.leaderstats["Coins"].Value = player.leaderstats["Coins"].Value -cost.Value 
            player.backpack.WeightLevel1.Value = player.backpack.WeightLevel1.Value + 1
            return true
    else
        cost.Changed:Connect(function()
                if cost.Value <= player.leaderstats["Coins"].Value then
            player.leaderstats["Coins"].Value = player.leaderstats["Coins"].Value -cost.Value 
            player.backpack.WeightLevel1.Value = player.backpack.WeightLevel1.Value + 1
            return true
            else
        return false
    end
        end)
    end
end