Socket.IO Error 400 when connecting to server, or never connects

I'm working on chat app, I have Android version made in Flutter, where Socket.IO works fine. Now I'm making web app of this chat app. But when the app tries to connect to server, the error is thrown: WebSocket connection to 'ws://localhost:3000/socket.io/?EIO=4&transport=websocket' failed: Error during WebSocket handshake: Unexpected response code: 400

Here is client code (I'm using React):

console.log("Connecting to websocket...");
this.socket = io(this.serverUrl(), {
    transports: ["websocket"],
    autoConnect: false
});
this.socket.on("connection", (data) => {
    console.log("Connected webscoket.");
    this.socket.emit("join", { token: this.token });
});
this.socket.connect();

Here is server code (Node.js), (The code is not complete, of course):

const express = require("express");
const app = express();
const http = require("http").createServer(app);
const port = process.env.PORT;
const io = require("socket.io")(http);

http.listen(port, () => {
    console.info("Server is running on port " + port);
});
io.on("connection", async (socket) => {
    console.log("Connected socket.io client " + socket.id);
});
socket.on("disconnect", async (reason) => {
    console.log("Socket disconnected");
});

I also tried to add origins like this:

const io = require("socket.io")(http, {
    origins: ["http://localhost:3001"]
});

Then the error is not there, but it never connects, and server console output looks like this:

Server is running on port 3000
Connected to database
Connected socket.io client QkoLREixPEyNglK7AAAA
Connected socket.io client QkoLREixPEyNglK7AAAA
Socket disconnected
Connected socket.io client C-j2N_Bvz8QDEQKUAAAB
Connected socket.io client C-j2N_Bvz8QDEQKUAAAB
Socket disconnected
Connected socket.io client 4Q6vxnNJb0gR-rVtAAAC
Connected socket.io client 4Q6vxnNJb0gR-rVtAAAC
Socket disconnected
Connected socket.io client g7MMXfwBuqjtS31_AAAD
Connected socket.io client g7MMXfwBuqjtS31_AAAD
Socket disconnected
Connected socket.io client NIquCegqW9yygXkIAAAE
Connected socket.io client NIquCegqW9yygXkIAAAE
...

Also the Android app stop working this way.

Thank you for all your answers.