127.0.0.1 is the local loopback interface. It will only be accessible from the server itself. If you need to access it remotely, start the app using:

flask run --host=0.0.0.0

This tells it to bind to all interfaces, including the public network. This will make it available at your public IP address on port 5000.

Do keep in mind this important note from the Flask documentation about why it defaults to running locally:

If you run the server you will notice that the server is only accessible from your own computer, not from any other in the network. This is the default because in debugging mode a user of the application can execute arbitrary Python code on your computer.