They mean to put that url in the address bar. For example, if I wanted to point my browser to fcc, I would put www.freecodecamp.org in the address bar.
This:
Then point your browser to your-app-url/json , you should see the message on the screen.
is telling you to do that for your app.
But I can’t do that with you app. When I get your server address and try to do that with https://boilerplate-express-2.raymondguo007.repl.co/json, I get an error.