Forge Tunnel exits immediately without error

I am starting to work through the Forge Tutorial. I can deploy and install my app, but when I start Forge Tunnel, it exits immediately. I have tried using the --verbose flag without any additional information.

I just get the following:

[root@localhost hello-world-app]# forge tunnel
Tunnel redirects requests you make to your local machine. This occurs for any Atlassian site where your app is installed in the development environment. You will not see requests from other users.
Press Ctrl+C to cancel.

Checking Docker image... 100%
Your Docker image is up to date.
Rerunning the command with --verbose may give more details.

What am I doing wrong?