help with sending notifications with remoteevents?

Okay, so what I wanted to do is to make it so that if an admin pressed an Imagebutton, a notification gui would pop up on the screens of every client on the server. This is what I have so far: local

event.OnClientEvent:connect(function()
    local notification = game.Players.LocalPlayer.PlayerGui:WaitForChild("notification"):WaitForChild("notification")
    notification:TweenPosition(UDim2.new( 0.312, 0, 0.686, 0), "In", "Sine", 0.5)
end)

post.MouseButton1Click:connect(function()
    event:FireServer()
end)

server

local event = game.ReplicatedStorage:WaitForChild("RemoteEvent")

event.OnServerEvent:connect(function()
    event:FireAllClients()
end)

The problem is when the admin clicks on the imagebutton that is supposed to move the notificationgui to everyone's screens, it only moves it on their own screen. (btw. the notificationgui is in StarterGui, so everyone has it already)