You'll need to initialize the web app in order to make yourself the admin. You can do this by going to the /init URL
in this web app.
At initialization you'll be required to enter a SendGrid API key. On localhost you can enter a fake API key (just a random string) because you'll be able to read emails in the Terminal. But on production use the real API key. For this you'll need to first create yourself a SendGrid account (their free tier would do).