Before you can use the app, you need to complete the following steps.

1. Create a tunnel to your localhost by running yarn lt --port 3000 --subdomain checkout-example. This tunnel lets the app handle the redirect to the success, failure, or cancellation page.
2. Build and serve the app by running yarn dev. The app is built in development mode. Wait for a message similar to the following to appear in your terminal:

     Waiting for file changes
     Memory usage: 606 MB (RSS: 736 MB)
     Listening on: http://localhost:3000
   

   Next, follow the steps in Using the app.