Error trying to diff '[object Object]'. When fetched data using ID

Ionic Framework ionic-v3
1

I got trouble when fetched from the database. Show this error in my console “Error trying to diff ‘[object Object]’. Only arrays and iterables are allowed”.

I want to fetch data by id or username.

this is my JSON :

{ id: "362a7e6c-8804-11ea-8211-00ffc8371d5a", content: "blablabla", roomid: "RM001", roomname: "IT GROUP", username: "JUSER", …}

  content: "blablabla"
  createdby: "0878668888"
  createdon: "2020-04-26T21:23:45.000Z"
  id: "362a7e6c-8804-11ea-8211-00ffc8371d5a"
  modifiedby: "0878668888"
  modifiedon: "2020-04-26T21:23:45.000Z"
  roomid: "RM001"
  roomname: "IT GROUP"
  username: "JUSER"
   __proto__: Object

my providers (chat-list-provider.ts) :

    getChatById(username) {
      return new Promise((resolve,reject) => {
        let header = new Headers();
        header.append('Content-Type', 'application/json');
  
        this.http.get('http://localhost:3001/api/messages/' + username, {headers: header})
        .map(res => res.json())
        .subscribe(_data => {
          resolve(_data);
        }, err => {
          reject(err);
        })
      })
    }

chat-list.ts

export class ChatListPage {
  public items: any = [];
  username = 'JUSER';

  constructor(
    public navCtrl: NavController, 
    public navParams: NavParams,
    private socket: Socket, 
    public chatListService: ChatListProvider,
    public modalCtrl: ModalController,
    public toastCtrl: ToastController,
    public http: Http) {
  
  }

  ionViewDidLoad() {
    this.getChatById(this.username);
  }

  getChatById(username) {
      this.chatListService.getChatById(username)
        .then((res) => {
          console.log(res);
          this.items = res;
          console.log(this.items);
       })
   }

My View :

<ion-content fullscreen>
  <ion-list>
    <ion-list-header>
      Conversations
    </ion-list-header>
    
    <ion-item *ngFor="let item of items" (click)="openMessage()">
      <ion-avatar slot="start">
        <img src="./avatar-finn.png">
      </ion-avatar>
      <ion-label>
        <h2>{{ item.roomname }}</h2>
        <p>{{ item.content }}</p>
      </ion-label>
    </ion-item>
  </ion-list>
</ion-content>

Please inform me if you found any wrong in my codes. Thanks