The page you are looking at is being generated dynamically by CodeIgniter.

If you would like to edit this page you'll find it located at:

application/views/welcome_message.php

The corresponding controller for this page is found at:

application/controllers/Welcome.php

This is example get from rest client:

string(1130) "

404 Page Not Found

The page you requested was not found.

"

This is example get new api key:

cggk8k0csog4kwksow8sko444w0ooko0kkws4csg

If you are exploring CodeIgniter for the very first time, you should start by reading the User Guide.