[Fizzlemizz]

You don't tell us what the error says which would be helpful but...

The SLASH_NOVIDADE1, SLASH_NOVIDADE2 etc. are for different slash commands that call the same function (in case one gets overwitten by another addon or you want to have say, a full addon name command and an acronym command (but you only need one) eg.:

SLASH_NOVIDADE1 = "/novidade"
SLASH_NOVIDADE2 = "/nvd"

if NOVIDADE_ToggleFrame is defined as a local function, it needs to be declared before the SlashCmdList entry is created

local function NOVIDADE_ToggleFrame()
    MyFrame:SetShown(not MyFrame:IsShown ())
end
 
SlashCmdList["NOVIDADE"] = function(msg)
     NOVIDADE_ToggleFrame()
end

I have no idea what the NOVIDADE_ToggleFrame function does so the code is just for exmple.