Can't read websocket on angular

I am trying to exchange info through websockets between an Angular 8 app and a simple server. Strangely I'm able to send info to the server, but I can't seem to find how to wire the app to receive back my echoes.

Here's the app component :

import { Component } from '@angular/core';
import { webSocket, WebSocketSubject } from "rxjs/webSocket";

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {

  ws : WebSocketSubject<any>;

  ngOnInit() {}

  constructor() {
    this.ws = webSocket('ws://localhost:8999');
    this.ws.subscribe({
      next : (data) => console.log(`Received ${data}`),
      error : (err) => {},
      complete : () => {}
    });
  }

  buttonClick() {
    this.ws.next("test");
  }

}

Here's the server :

import * as express from 'express';
import * as http from 'http';
import * as WebSocket from 'ws';

const server = http.createServer(express());

const wss = new WebSocket.Server({ server });

wss.on('connection', (ws: WebSocket) => {
    // Print and echo
    ws.on('message', (data) => {
      console.log(`received: ${data}`);
      ws.send(`echo: ${data}`);
    })
});

setInterval(() => wss.clients.forEach(ws => ws.send(`ping!`)), 2000);


// Start server
server.listen(process.env.PORT || 8999, () => {
    console.log(`Server started on port ${(<WebSocket.AddressInfo>server.address()).port}`);
});

And testing the server with a simple tool at least confirms me that side is working

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