When you create an EC2 Cloud9 instance, out of the box your preview will only be available in your native browser. IE it will be unavailable to anyone else you send the link to and you also will not be able to work with applications like Postman.
To make the application publicly available follow two steps.
Modify the app.listen() listening port in your application to the remove the IP Address. I will look something like this
// set listen port
After you’ve made the server public you can always remind yourself of the IP address for sharing by clicking on the share button inside your IDE, which will then show you the application IP. You will need to tack the port onto the end of the IP listed here. Ex:
This will be the publicly available address for whichever application you are running on this instance (assuming you have more than one application on the instance)