How to Fix Warning: "Prestashop _PS_MODE_DEV_ is active" - Amazon Marketplace Plus

When accessing the information page of the Amazon Marketplace Plus module, you may encounter the following diagnostic warning message:

Prestashop _PS_MODE_DEV_ is active

Why Does This Warning Occur?

The _PS_MODE_DEV_ constant is PrestaShop's native Development/Debug Mode setting. While highly valuable during website building or troubleshooting, leaving it active on a live production storefront introduces major issues:

1. Severe Security Risk: If any error occurs on your site, PrestaShop will display full technical details to your visitors, including your database structure, absolute server file paths, and vulnerable code lines.
2. Performance Drop: Debug mode prevents certain asset caching mechanisms, which slows down page loading times for your customers.
3. Module Synchronization Failures: Extra notices or warnings triggered in debug mode can leak into background AJAX/JSON payloads, breaking the module's automated connection with Amazon.

How to Resolve the Warning

You can disable debug mode directly from your admin panel or manually via server files if the back office is inaccessible.

Method 1: Disable Debug Mode via PrestaShop Back Office (Recommended)

This is the easiest and most common way to turn off debug mode:

1. Log into your PrestaShop back office.
2. In the left menu, navigate to Advanced Parameters > Performance.
3. Locate the Debug mode section near the top of the page.
4. Set the Debug mode toggle to No.
5. Click the Save button in the top right corner.

Method 2: Update the Configuration File (Alternative via FTP)

If you cannot access your back office, you can disable it through your site's files:

1. Connect to your server using an FTP client or your hosting File Manager.
2. Navigate to the root directory of your PrestaShop installation.
3. Open the config folder and open the file named defines.inc.php.
4. Locate the following line of code (usually near line 28):

define('_PS_MODE_DEV_', true);

5. Change its value from true to false:

define('_PS_MODE_DEV_', false);

6. Save the file and upload it back to your server.

Updated on: 04/06/2026