SignalR multiple chat rooms with Angular and .Net

Question

Good I have a question when I send to all users let me go well, but when I limit it to only users who are in certain groups by passing the Id of the room directly I do not get anything directly from the Hub, the truth is that I do not know what can be I'm doing wrong.

BackEnd

[HttpPost]
public IActionResult SendMessage([FromBody] MessagesForCreationDto message)
{

    if (message == null)
    {
        
            _logger.LogError("Message object sent from client is null.");
            return BadRequest("Message object is null");
    }

    message.Room = Convert.ToString(message.FK_ChatRoomID);


    var messages = _mapper.Map<Messages>(message);

    _repository.Messages.Create(messages);

    _repository.Messages.SaveAsync();

    string not = Newtonsoft.Json.JsonConvert.SerializeObject(message);

     //_hubContext.Clients.Group(message.Room).SendAsync("ReceiveMessage", not);

    _hubContext.Clients.All.SendAsync("ReceiveMessage", not);

    return Ok();
}

FrontEnd

Service

 export class ChatService extends DataService {
  public hubConnection: HubConnection;
  messageReceived: EventEmitter<Messages> = new EventEmitter();

  constructor(http: HttpClient) {
    super(http, '/chatrooms');

    console.log('Inicio el servicio signal con cambio');

    const builder = new HubConnectionBuilder();
    this.hubConnection = builder.withUrl('https://localhost:5001/chat').build();

    this.hubConnection.on('ReceiveMessage', (mensaje) => {
      const not: Messages = JSON.parse(mensaje);
      this.messageReceived.emit(not);

      console.log(mensaje);
    });
    this.hubConnection.start();
  }
}

Ts

    msj: Messages[] = [];

  getById() {
    this.handler = this.chatService.getById(this.id).subscribe(data => {
      this.chat = data;
      this.msj.push(...this.chat.messages);
      console.log(data);
    }, error => {
      console.log(error);
    });
  }