Development Mode - Just For You.

In config.local.php

Add this code directly underneath the copyright notice:

if ($_SERVER['REMOTE_ADDR'] == '') {
define('DEVELOPMENT', true);
ini_set('display_errors', 'On');

Where equals your IP address.

This will allow you to review any error messages when displayed, and not to your customers.

Also, it might be a good idea to activate the debugger for both the admin panel and the storefront. Just add the following line:

define('DEBUG_MODE', true);

after this one:

ini_set('display_errors', 'On');

You can check more information about bult-in debugger here:

Debugger — CS-Cart 4.2.x documentation