1. 确保您已正确配置Firebase和FCM。确保您具有正确的Firebase配置，并已获取正确的服务器密钥。确保您的应用程序专用于FCM并已正确配置。
2. 如果您想在生产环境中使用FCM，则应该通过Service Worker注册推送通知。在/src/app/app.module.ts文件中，添加以下代码片段：

import { enableProdMode } from '@angular/core';
import { environment } from './environments/environment';

if (environment.production) {
  enableProdMode();
  
  if ('serviceWorker' in navigator) {
    window.addEventListener('load', () => {
      navigator.serviceWorker.register('/firebase-messaging-sw.js')
        .then(registration => {
          firebase.messaging().useServiceWorker(registration);
        })
        .catch(error => console.error(error));
    });
  }
}

3. 确认您已正确订阅消息。在您的组件中，添加以下代码片段，以在Firebase Cloud Messaging发出推送通知时监听消息：

import { AngularFireMessaging } from '@angular/fire/messaging';
import { BehaviorSubject } from 'rxjs';

@Injectable()
export class MessagingService {
  private messageSource = new BehaviorSubject(null);
  currentMessage = this.messageSource.asObservable();

  constructor(private angularFireMessaging: AngularFireMessaging) {
    this.angularFireMessaging.messages.subscribe(
      (payload) => {
        console.log("new message received. ", payload);
        this.messageSource.next(payload);
      });
  }
}

4. 确保您已正确配置FirebaseMessagingService。在/app/app.module.ts文件内，按照以下方式导入Firebase相关模块：

import firebase from 'firebase/app';
import 'firebase/messaging';
import { AngularFireMessagingModule } from '@angular/fire/messaging';

@NgModule({
  imports: [
    AngularFireMessagingModule,
    ...
  ],
  providers: [
    ...
    {
      provide: AngularFireMessaging,
      useFactory: firebaseMessagingStub
    }
    ...
  ],
})
export class AppModule { }

export function firebaseMessagingStub() {
  return {
    requestPermission: () => new Promise((resolve, reject) => {}),
    getToken: () => new Promise((resolve, reject) => {}),
    onMessage: () => new Observable()
  };
}

通过这些步骤，您应该能够正确地实施FCM推送通知并使其工作。