On / Off Mute Button Values Not Changing?

Hi folks, I know I've already asked about 100 questions (Kidding, but it feels like it) but as a novice I still pick up new things and new errors along the way. Cutting to the chase, I have this code for my game in which I would like people to have the option to turn music on or off in game, but when I click the button it doesn't want to work. Please take a look at what I've tried.

script.Parent.MouseButton1Down:Connect(function()
    IsOn = true
    if IsOn == true then
        for i,v in pairs (script.Parent.Parent.TextButton:GetChildren())do
            if (v.ClassName == "Sound") then
                v.Volume = 1
                script.Parent.Image = "rbxassetid://205571713"
            elseif IsOn == not false then
                IsOn = false
            end
        end
        end
            script.Parent.MouseButton1Down:Connect(function()
            IsOn = false
            if IsOn == false then
            for i,v in pairs (script.Parent.Parent.TextButton:GetChildren())do
            if (v.ClassName == "Sound") then
                v.Volume = 0
                script.Parent.Image = "rbxassetid://205571728"
            elseif IsOn == not true then
                IsOn = true
            end
            end
        end
    end)
end)

Any help would be very much appreciated, thank you all so kindly for your time and effort. I hope to hear from you soon!