Run npm start.

Browser console will print:

[ERROR] 43:49.211 AuthError -
        Error: Amplify has not been configured correctly.
        The configuration object is missing required auth properties.
        This error is typically caused by one of the following scenarios:

        1. Did you run `amplify push` after adding auth via `amplify add auth`?
            See https://aws-amplify.github.io/docs/js/authentication#amplify-project-setup for more information

        2. This could also be caused by multiple conflicting versions of amplify packages, see (https://docs.amplify.aws/lib/troubleshooting/upgrading/q/platform/js) for help upgrading Amplify packages.