Hi @tomaston
Thank you for using our plugin.
We apologize for the inconvenience.
Actually we used it for objects.
Please clear your cart products and then add some products to the cart to test it.
Maybe you have a plugin that modify cart objects, to find it please follow the below instructions.
- Deactivate all of WooCommerce related plugins and only active our plugin with WooCommerce.
- Delete all of cart items.
- Try to add some products to the cart and try it.
- If error gone, you can activate other WooCommerce related plugins one by one to find the plugin that causes the issue.
If the error persists, you can contact us here, and send us full error message.
I hope it helps.
Best Regards