Socketio undefined results - node.js

Question

a few days ago I tried to train with react by creating a real-time chat application, but I'm a bit lost in the io socket, I can't send a message or notification on a specific user, I get an "undefined" error, here is my socket io code:
I tried to retrieve the user with the id as receiverId but socket io returns me undefined
about this function:
socket.on("friendRequest", ({ senderId, receiverId }) => { const receiver = getUser(receiverId); console.log(receiver) });
How can I fix this error,
thank you very much
And sorry for my English,
const express = require('express');
const socketio = require('socket.io');
const http = require('http');
const cors = require('cors');
const PORT = process.env.PORT || 5000;
const router = require('./router');
//const { Socket } = require('dgram');
const app = express();
const server = http.createServer(app);
const io = socketio(server);
app.use(router);
app.use(cors());
let users = [];
const addUser = (userId, socketId) => {
!users.some((user) => user.userId === userId) &&
users.push({ userId, socketId });
};
const removeUser = (socketId) => {
users = users.filter((user) => user.socketId !== socketId);
};
const getUser = (userId) => {
return users.find((user) => user.userId === userId);
};
io.on('connect', (socket) => {
console.log("a user connected.");
socket.on("addUser", (userId) => {
addUser(userId, socket.id);
io.emit("getUsers", users);
});
socket.on("sendNotification", ({ senderId, receiverId, type }) => {
const receiver = getUser(receiverId);
io.to(receiver.socketId).emit("getNotification", {
senderId,
type,
});
});
socket.on("friendRequest", ({ senderId, receiverId }) => {
const receiver = getUser(receiverId);
console.log(receiver)
});
socket.on("sendText", ({ senderId, receiverId, text }) => {
const receiver = getUser(receiverId);
io.to(receiver.socketId).emit("getText", {
senderId,
text,
});
})
socket.on("disconnect", () => {
console.log("User Disconnected", socket.id);
removeUser(socket.id);
io.emit("getUsers", users);
});
});
app.use(router);
server.listen(PORT,() => console.log('Server has started on port ${PORT}'));```