irst ensure that there is no place in your code where you set error_reporting to 0 e.g.
error_reporting(0);
as this will totally hide all error warnings and notices.
In php script, this three line of code will just turn it on
ini_set('display_errors', 1);
ini_set('display_startup_errors', 1);
error_reporting(E_ALL);
You should see the same messages in the PHP error log.
Other things that you will need to check
1.) PHP.INI Files or your Apache configurations
You can move to your php.ini files and ensure that the following parameters below are commented out and set on.
By commented out, I mean removing a semicolon**(;)** at back of it
Eg.
uncomented = ;display_errors=On
commented = display_errors=On // semicolon removed
display_errors=On
display_startup_errors=On
track_errors = On
html_errors=On
shutdown and restart apache for it to take effect.
2.) .HTACCESS Files
You can also check .htaccess files to see if any of these warning parameter flags are set to 0 which means off and set them to 1 which means On.
Remember to turn off all these error warnings in production.