WooCommerce Checkout Not Working: A Technical Debugging Checklist

When a WooCommerce checkout fails to load, spins indefinitely, or blocks payments, the root cause is almost always a JavaScript conflict, aggressive caching, or server-level security blocks. Use this structured checklist to diagnose and fix the issue.

1. Inspect the Browser Console for JavaScript Errors

WooCommerce relies heavily on AJAX to update checkout fragments and process payments. If a script fails, the checkout process halts.

• Open your checkout page, right-click, and select Inspect (or press F12).
• Navigate to the Console tab.
• Look for red error messages. If you see errors related to checkout.min.js or jQuery, a plugin or theme script is breaking the execution.
• If you are deferring jQuery or using optimization plugins (such as WP Rocket, LiteSpeed Cache, or Autoptimize), temporarily disable JavaScript minification/deferral to see if the issue resolves.

2. Verify AJAX Endpoint Status (wc-ajax)

WooCommerce uses the /?wc-ajax=checkout or /?wc-ajax=update_order_review endpoints to process orders. If these return a 403, 404, or 500 error in the Network tab:

• 403 Forbidden: A security plugin (like Wordfence or Sucuri) or a server firewall (like ModSecurity) is blocking the AJAX request. Whitelist the WooCommerce AJAX endpoints in your firewall settings.
• 500 Internal Server Error: Check your server's PHP error logs (usually error_log in your site root or via your hosting panel) to find the exact PHP fatal error.

3. Exclude Checkout Pages from Caching

Caching the checkout or cart page causes session mismatches, empty carts, and failed transactions. Ensure your caching plugin, CDN (Cloudflare), or server-side cache (Varnish, Redis, Nginx FastCGI) excludes these URIs:

/cart/*
/checkout/*
/my-account/*

Additionally, ensure that the cookie woocommerce_items_in_cart bypasses page caching entirely.

4. Increase PHP Memory Limit

Complex checkouts with multiple shipping gateways, tax calculations, and discount codes can exhaust PHP memory, leading to silent failures during order processing. Add this line to your wp-config.php file to increase the limit to 256MB or higher:

define( 'WP_MEMORY_LIMIT', '256M' );

5. Perform a Theme and Plugin Conflict Test

If the issue persists, isolate WooCommerce from third-party code:

• Install the Health Check & Troubleshooting plugin by the WordPress community. This allows you to test without affecting live visitors.
• Enable Troubleshooting Mode, which switches your theme to a default theme (like Storefront or Twenty Twenty-Four) and disables all plugins only for your user session.
• Test the checkout. If it works, re-enable plugins one by one until the checkout breaks to identify the culprit.

6. Check SSL and Mixed Content Issues

Modern payment gateways require a secure connection. If your site has mixed content (loading HTTP assets on an HTTPS page), the gateway API will fail.

• Go to Settings > General and verify that both the WordPress Address (URL) and Site Address (URL) start with https://.
• Use a plugin like Better Search Replace to replace instances of http://yourdomain.com with https://yourdomain.com in your database if you recently migrated to SSL.

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