Just as a favor to anyone out there that may be experiencing this issue with WooCommerce as of 2.4, I wanted to post the solution that we found. I’m sure this won’t be the end-all solution for everyone, but it may help some of you.
WooCommerce Checkout Not Working Upon Update
Check that your payment gateway isn’t using this method:
For some reason, using that method had always worked in the past, but now was triggering some non-JSON responses upon checkout. Instead, manually update the stock levels and status like so:
$order->update_status('processing', __( 'Awaiting fulfillment.', 'woocommerce' )); // Reduce stock levels $order->reduce_order_stock(); // Remove cart WC()->cart->empty_cart();
Hope this saves someone a lot of headache!