Erro na hora de abrir o XMLHttpRequest

Eu me deparei com esse erro na aula 3, eu fiz exatamente como na aula, não entendi oque deu errado, alguém pode me ajudar?

app.component.ts

import { Component } from '@angular/core';
import { PhotoService } from './photos/photo/photo.service';


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


  constructor(photoService: PhotoService) {

  photoService
  .listFromName('flavio')
  .subscribe(photos => this.photos = photos);
  }

}

photo.service.ts

import { HttpClient } from "@angular/common/http";
import { Injectable } from "@angular/core";

const API = 'http://localhost:3000';

@Injectable({providedIn:'root'})
export class PhotoService {

    constructor(private http: HttpClient){}

        listFromName(userName: string){

            return this.http
            .get<object[]>(API + './flavio/photos');

        }
}