Every UWP app submitted to the Windows Store will be validated by Microsoft before being listed for the general public. Part of that validation process involves running the app through an automatic certification tool that Microsoft has included with Visual Studio. You should verify that your app passes the certification tool before beginning the Windows Store submission process.
You will need a packable UWP app to complete this recipe. You may either reuse the RSSReader
app described in the Packaging your UWP app recipe, or use a UWP app of your own choice. Either way, ensure that you have a UWP app that is working correctly and deployable in Release mode.
The following steps need to be performed in order to validate your app for the Windows Store:
From the Windows Start screen, launch the Windows App Cert Kit. (If you are following directly from the Packaging your UWP app recipe, you can launch the kit from the Package Creation Completed...