Set up but...

First off - don't modify core/Common.php. Never a good idea to modify core files, especially when this has nothing to do with that.

Look at the error message: "Cannot modify header information - headers already sent by (output started at /Applications/MAMP/htdocs/application/controllers/Pages.php:20)" That tells you approximately where the output happened.

But to understand what's going on - some part of your code output something (even a space would do it) before CodeIgniter sent the headers to the browser. This error would show up in a number of common situations, like:

- space (or other characters) before the opening PHP tag in a PHP file (easy to accidentally do if you forgot to switch to the console before you started typing. Yeah, that's from experience.
- you echo something out, do a var_dump, print_r, etc for debugging.

So start looking around line 20 of your Pages controller for something that may be spitting out text.

Support Development •  CodeIgniter 4 Foundations • Practical CodeIgniter 3  • CodeIgniter Tutorials