If you navigate to the Preview section, you will see an iPhone in the browser and a Unique ID number. Enter this Unique ID in the iPhone, and you will be able to preview and test your app directly in browser:

This document covers the procedure of previewing your app with the React Builder of apprat.io
If you navigate to the Preview section, you will see an iPhone in the browser and a Unique ID number. Enter this Unique ID in the iPhone, and you will be able to preview and test your app directly in browser: