Dialog works for one NPC, but stops working for any other NPC?((only works onetime))

function startconvo()
    print("conversation started")

    char.Humanoid.WalkSpeed = 0 --freeze player
    char.HumanoidRootPart.Anchored = true

    readoptions(script.Greeting) --generate table of all options

    convogui.Parent = script.Parent --show the gui
    chat(script.Greeting.Value) --display greeting
    local options = script.Greeting:GetChildren()
    wait(displaytime)
    makebuttons(options) --generate buttons
end

--end conversation
function endconvo()
    print("conversation ended")
    --clean up options
    for i,v in pairs(convogui.Frame.Selections:GetChildren()) do
        v:Destroy()
    end
    wait(displaytime)
    convogui:Destroy() --remove the gui
    char.Humanoid.WalkSpeed = 16 --unfreeze player
    char.HumanoidRootPart.Anchored = false
    sound:Destroy() --remove the sound
end

--==========have a conversation

startconvo()

this portion here is incharge of starting the convo and ending it, this is at the end of the script, and generally after the "converstaion ended" for one NPC, it doesnt work for another NPC, it only works once for only one NPC, after that you cannot start a conversation with any other NPC? Any reason why?

no logs or anytihng to show an error.