“Cart simulation failed: Could not validate nonce” every minute on live site

Hello @vanderk ,

Thank you for your detailed report and for sharing all the context — this really helps a lot in narrowing things down.

I’ve reviewed your case along with similar reports, and I’d like to clarify what’s happening and address your questions directly.

What this error actually means

The log message: “Cart simulation failed: Could not validate nonce” is not the root cause of an issue, but rather a warning generated during a background process.

The PayPal plugin performs a cart simulation in the background to calculate totals before creating an order. If that request runs without a valid session/nonce, the validation fails and the log entry is created. This commonly happens due to:

• Cached or stateless requests
• Expired sessions
• Background calls (not real user actions)

1. Is this expected behavior or a real problem?

Based on:

• Your successful live transactions
• No checkout failures reported
• The errors occurring regularly even without users

This is generally considered non-blocking behavior and can often be safely ignored from a functional standpoint. These logs are not necessarily tied to failed payments and are often just noise from background validation.

2. Are there known issues with your plugin version?

There are no confirmed widespread regressions tied specifically to your version (4.0.2) regarding this error. However, similar reports across versions indicate:

• The message appears frequently in logs
• It is usually not the root issue, but a side effect of caching or session handling

3. Can this be disabled or adjusted?

There is no official setting to fully disable cart simulation, as it’s part of how PayPal keeps totals accurate. However, you can try this PHP snippet on a staging/test website:

add_filter( 'woocommerce_paypal_payments_simulate_cart_enabled', '__return_false' );

However, it’s not guaranteed to resolve the logs and is generally not recommended unless needed for testing.

Recommended next steps

To confirm the source, we suggest:

1. Temporarily enable Cloudflare Development Mode (or pause it briefly)
2. Disable WP Rocket for a few minutes
3. Monitor logs for 5–10 minutes

If logs stop, it confirms a caching layer is triggering these requests. If everything is working fine on the checkout side, then this is very likely just log noise from background processes.

Please note that within this forum, we focus on supporting WooCommerce core functionality. Since this behavior originates from the WooCommerce PayPal Payments plugin, the best place for deeper investigation or plugin-specific fixes would be their dedicated support channel:
https://wordpress.org/support/plugin/woocommerce-paypal-payments/

That said, if you notice any issues directly related to WooCommerce core features, please don’t hesitate to let us know — we’ll be more than happy to assist.

Best regards,
Mina Emad