(ChatService) How to fix nil MuteSpeaker?

local ChatService = require(game:GetService("ServerScriptService"):WaitForChild("ChatServiceRunner").ChatService)

local channel = ChatService:GetChannel("All")

channel:MuteSpeaker(game.Players.sayer80.Name,"A ghost can't talk...")

Error:

channel:MuteSpeaker(game.Players.sayer80.Name,"A ghost can't talk..."):6: attempt to index nil with 'MuteSpeaker' 

I've looked through https://developer.roblox.com/, asked on HD and Scripting Helpers Discord, but no one can help me.

I want to create a few lines of code that can Mute a Player from the chat, making him unable to write, but still being able to view the chat, also later being able to unmute the Player.

I've done 0 modifications to the chat.