Use Component From Shared Module Of A Sub Angular App (nested apps)

Question

I have nested Angular Apps:

MainApp { 
   projects:{
     App1,
     App2
   }
}

I want to use a Component from Sub App (App1), in my (MainApp). Here is my (MainApp) app.module.ts:

 imports: [
    BrowserModule,
    AppRoutingModule,
    App1SharedModule.forRoot(),
    App2SharedModule.forRoot()
  ],

I've got Error Message: 'app-xxx' is not a known element:

Any suggestions ?