title: Error message while trying to build --Ionic App
body: <p>Its my first time trying to build app with slide and login before tab, I'm getting this error message below from the slide components and the start while trying to build
  with
  ionic build --prod. I think I needed to add some module, like CUSTOM_ELEMENTS_SCHEMA can someone tell me how and where</p>
  <pre><code>ERROR in src/app/components/slides/slides.component.html:1:1 - error NG8001: 'ion-content' is not a 
  known element:
  1. If 'ion-content' is an Angular component, then verify that it is part of this module.
  2. If 'ion-content' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' 
  of this component to suppress this message.
  
  1 &lt;ion-content&gt;
  
  src/app/components/slides/slides.component.ts:5:16
  5   templateUrl: './slides.component.html',
                   ~~~~~~~~~~~~~~~~~~~~~~~~~
  </code></pre>
  <p>Error occurs in the template of component SlidesComponent.
  src/app/components/slides/slides.component.html:2:3 - error NG8001: 'ion-slides' is not a known
  element:
  1. If 'ion-slides' is an Angular component, then verify that it is part of this module.
  2. If 'ion-slides' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of
  this component to suppress this message.</p>
  <pre><code>2   &lt;ion-slides pager=&quot;true&quot; [options]=&quot;slideOpts&quot;&gt;
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  
  src/app/components/slides/slides.component.ts:5:16
  5   templateUrl: './slides.component.html',
                   ~~~~~~~~~~~~~~~~~~~~~~~~~
  Error occurs in the template of component SlidesComponent.
  src/app/components/slides/slides.component.html:2:28 - error NG8002: Can't bind to 'options' since it 
  isn't a known property of 'ion-slides'.
  1. If 'ion-slides' is an Angular component and it has 'options' input, then verify that it is part of 
  this module.
  2. If 'ion-slides' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of 
  this component to suppress this message.
  3. To allow any property add 'NO_ERRORS_SCHEMA' to the '@NgModule.schemas' of this component.
  
  2   &lt;ion-slides pager=&quot;true&quot; [options]=&quot;slideOpts&quot;&gt;
                           ~~~~~~~~~~~~~~~~~~~~~
  
  src/app/components/slides/slides.component.ts:5:16
  5   templateUrl: './slides.component.html',
                   ~~~~~~~~~~~~~~~~~~~~~~~~~
  Error occurs in the template of component SlidesComponent.
  src/app/components/slides/slides.component.html:3:5 - error NG8001: 'ion-slide' is not a known 
  element:
  1. If 'ion-slide' is an Angular component, then verify that it is part of this module.
  2. If 'ion-slide' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of 
  this component to suppress this message.
  
  3     &lt;ion-slide&gt;
    ~~~~~~~~~~~
  
  src/app/components/slides/slides.component.ts:5:16
  5   templateUrl: './slides.component.html',
                   ~~~~~~~~~~~~~~~~~~~~~~~~~
  Error occurs in the template of component SlidesComponent.
  src/app/components/slides/slides.component.html:8:5 - error NG8001: 'ion-slide' is not a known 
  element:
  1. If 'ion-slide' is an Angular component, then verify that it is part of this module.
  2. If 'ion-slide' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of 
  this component to suppress this message.
  
  8     &lt;ion-slide&gt;
    ~~~~~~~~~~~
  
  src/app/components/slides/slides.component.ts:5:16
  5   templateUrl: './slides.component.html',
                   ~~~~~~~~~~~~~~~~~~~~~~~~~
  Error occurs in the template of component SlidesComponent.
  src/app/components/slides/slides.component.html:12:5 - error NG8001: [0m'ion-slide' is not a known 
     element:
  1. If 'ion-slide' is an Angular component, then verify that it is part of this module.
  2. If 'ion-slide' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of 
  this component to suppress this message.
  
  12     &lt;ion-slide&gt;
     ~~~~~~~~~~~
  
  src/app/components/slides/slides.component.ts:5:16
  5   templateUrl: './slides.component.html',
                   ~~~~~~~~~~~~~~~~~~~~~~~~~
  Error occurs in the template of component SlidesComponent.
  src/app/components/start/start.component.html:1:1 - error NG8001: 'ion-button' is not a known 
  element:
  1. If 'ion-button' is an Angular component, then verify that it is part of this module.
  2. If 'ion-button' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of 
  this component to suppress this message.
  
  1 &lt;ion-button expand=&quot;full&quot; color='secondary' (click)=&quot;navigateToLoginPage()&quot;&gt;Start&lt;/ion-button&gt;
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  
  src/app/components/start/start.component.ts:6:16
  6   templateUrl: './start.component.html',
                   ~~~~~~~~~~~~~~~~~~~~~~~~
    Error occurs in the template of component StartComponent.
  
   [ERROR] An error occurred while running subprocess ng.
  
      ng.cmd run app:build:production exited with exit code 1.
  
      Re-running this command with the --verbose flag may provide more information.
  </code></pre>