延迟加载时找不到模块错误

我想为模块设置延迟加载，但是有一个我无法解决的错误。

错误是：

core.js：15724错误错误：未捕获（已承诺）：错误：找不到模块'app / invoice-builder / invoice-builder.module'错误：无法找到模块'app / invoice-builder / invoice-builder.module'

app-routing.module.ts

import { NgModule } from '@angular/core';
import { Routes, RouterModule } from '@angular/router';

const routes: Routes = [
  {
    path: 'invoice-builder',
    loadChildren : 'app/invoice-builder/invoice-builder.module#InvoiceBuilderModule'
  },
  {
    path: '**',
    redirectTo: 'invoice-builder'
  }
];

@NgModule({
  imports: [RouterModule.forRoot(routes)],
  exports: [RouterModule]
})
export class AppRoutingModule { }

app.module.ts

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';

import { AppRoutingModule } from './app-routing.module';
import { AppComponent } from './app.component';

import {BrowserAnimationsModule} from '@angular/platform-browser/animations';
import { from } from 'rxjs';
import { MaterialModule } from './shared/material.module';


@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    AppRoutingModule,
    BrowserAnimationsModule,
    MaterialModule

  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }

我不明白这里发生了什么。我尝试使用两次重新启动项目，npm start但没有成功。任何帮助将非常感激。