Through FilterStringAsync, an instance (text filter result object) is returned.
To get the filtered text do this
local TextService = game:GetService("TextService")
local object = TextService:FilterStringAsync(message, fromPlayerId)
local filteredText = object:GetNonChatStringForBroadcastAsync()
Remember that these functions make web calls internally so it is ideal for them to be wrapped in protected calls (pcalls).