Client to Client connection, simple message doesnt work?

So I got my own House buying system where u can buy houses and enter them. Now I want to do it like that players who doesnt own the house can "ring the bell". If they do that a GUI will appear to the player who owns the house.

How can I do that? I tried it with the official and tried to come around it a bit but nothing worked

-- LocalScript

local ReplicatedStorage = game:GetService("ReplicatedStorage")
local Players = game:GetService("Players")

local player = Players.LocalPlayer
local playerGui = player:WaitForChild("PlayerGui")
local messageScreen = playerGui:WaitForChild("MessageScreen")
local recipientInput = messageScreen:WaitForChild("RecipientInput")
local sendButton = messageScreen:WaitForChild("SendButton")
local messageLabel = messageScreen:WaitForChild("MessageLabel")

local sendMessageEvent = ReplicatedStorage:WaitForChild("SendMessageEvent")

local function onSendButtonClicked()
    local recipientName = recipientInput.Text
    local recipient = Players:FindFirstChild(recipientName)
    if recipient then
        sendMessageEvent:FireServer(recipient)
    end
end

local function onMessageReceived(sender)
    messageLabel.Text = sender.Name .. " says hello!"
    messageLabel.Visible = true
    wait(3)
    messageLabel.Visible = false
end

sendButton.MouseButton1Click:Connect(onSendButtonClicked)
sendMessageEvent.OnClientEvent:Connect(onMessageReceived)