this notice
Use of undefined constant ROOT_PATH - assumed 'ROOT_PATH
shows pointing to this line define(ROOT_PATH, __DIR__);
the same one that I am using to include PHP files, because the warning is displayed, that I am doing wrong.
define(ROOT_PATH, __DIR__);
include ROOT_PATH . '/config.ini.php';
If you look at the PHP documentation , you will notice that the definition of constants is done in this way
So the error can occur depending on the fact that PHP has predefined constants in its core, so by not using quotes you cause the interpreter to search in the existing ones and since it is clearly not part of, it returns that error