Why does WooCommerce throw a 500 error during checkout specifically?

Checkout runs payment gateway API handshakes, taxes, and shipping calculations simultaneously. If memory drops below 256MB or a payment webhook times out, PHP halts with a fatal 500 error.

How do I resolve a 500 error caused by database session bloat?

Clear expired transients using WP-CLI (wp transient delete --expired) and truncate the wp_woocommerce_sessions table to release locked database threads.

WooCommerce 500 Internal Server Error: 9 Root Causes and Step-by-Step Fixes

A WooCommerce 500 Internal Server Error occurs when PHP crashes during request execution. The fastest diagnosis path is enabling WP_DEBUG in wp-config.php, inspecting /wp-content/debug.log, and verifying memory_limit (at least 512MB for WooCommerce) and plugin hook conflicts via WP-CLI.

What Does a 500 Error Mean in WooCommerce?

An HTTP 500 Internal Server Error is a catch-all status code indicating that the web server (LiteSpeed, Apache, Nginx) encountered an unrecoverable failure while attempting to execute a PHP script. Unlike 404 or 403 errors, a 500 error originates from server-side code execution — typically fatal PHP errors, exhausted memory, database timeouts, or corrupted server configuration files.

The 9 Most Common Root Causes and Solutions

1. Exhausted PHP Memory Limit

WooCommerce requires significant RAM during cart calculations, payment gateway callbacks, and inventory checks. A default memory_limit = 128M is insufficient. Increase the ceiling in wp-config.php:

define('WP_MEMORY_LIMIT', '512M');
define('WP_MAX_MEMORY_LIMIT', '512M');

2. Plugin Conflicts After Updates

Incompatible third-party WooCommerce extensions frequently attempt to invoke deprecated methods or trigger fatal namespace conflicts. Isolate the problematic plugin instantly using WP-CLI without touching the database:

wp plugin deactivate --all
# Then reactivate WooCommerce core first:
wp plugin activate woocommerce

3. Corrupted .htaccess Directives

Faulty redirect rules or syntax errors injected by caching plugins will trigger immediate 500 errors. Rename your .htaccess to .htaccess.bak and regenerate default WordPress rules via CLI:

wp rewrite flush --hard

4. Exceeded Maximum Execution Time

Complex catalog exports, bulk order updates, or webhook notifications that take longer than max_execution_time (typically 30 seconds) get killed by PHP. Elevate execution time limits in .user.ini or php.ini:

max_execution_time = 300
max_input_time = 300

5. Child Theme Syntax or Hook Errors

A fatal syntax error in functions.php immediately halts execution. Switch to the default Storefront theme to isolate theme-level issues:

wp theme activate storefront

6. PHP Version Incompatibility

Running legacy extensions on PHP 8.2 or 8.3 often triggers fatal deprecation exceptions. Verify your PHP error logs to identify unsupported code syntax.

7. MySQL Session Lock & Table Corruption

The wp_woocommerce_sessions table can accumulate millions of expired rows, locking the database during checkout. Clean transients and optimize tables:

wp transient delete --expired
wp db optimize

8. Missing or Corrupted WordPress Core Files

Interrupted updates can corrupt core files. Verify file integrity against official checksums:

wp core verify-checksums

9. Syntax Errors in wp-config.php

BOM markers (Byte Order Marks) or stray whitespace before the opening <?php tag in wp-config.php will trigger premature output headers and 500 crashes.