can't Preview the application in aws cloud9 when uses express application generator

For application preview and sharing instructions, see https://docs.aws.amazon.com/cloud9/latest/user-guide/app-preview.html

To summarize the preceding information...

To preview your running application, be sure to:

• Run using HTTP over port 8080, 8081, or 8082 with the IP of 127.0.0.1, localhost, or 0.0.0.0. (You don't have to use these ports or IPs. However, you won't be able to preview--skip ahead to the "to share..." part.)
• With the corresponding application code file open and active in the AWS Cloud9 IDE, choose one of the following on the menu bar: Preview, Preview Running Application --OR-- Tools, Preview, Preview Running Application.

To share your running application with others, be sure to:

• Set up the AWS Cloud9 development environment's associated Amazon EC2 security group to allow incoming HTTP requests over port 8080, 8081, or 8082. (Or whatever port the app is running on.)
• Set up the AWS Cloud9 development environment's associated network ACL in Amazon VPC to also allow incoming HTTP requests over port 8080, 8081, or 8082. (Or whatever port the app is running on.)
• Have others browse to your Amazon EC2 instance's public IP address. Be sure to start the URL with the correct protocol, add the port number if it is not the default for that protocol, and any other required URL components for your app (for example, /index.html, etc.).