[Seerah]

You don't fire the callback. FTC does. All you do is register for it and listen for when it happens. When it fires, your registered function will run. THAT is where you should be putting your code.

FTC code:

CALLBACK_MANAGER:FireCallbacks("FTC_Ready")

Your code:

local function CreateSubmenu()
     --do stuff
end
CALLBACK_MANAGER:RegisterCallback("FTC_Ready", CreateSubmenu)