Fix WooCommerce Checkout Payment Failure

The checkout on my WooCommerce store suddenly refuses to process credit / debit card payments—customers reach the final step but the transaction never completes. No error notices appear in WooCommerce logs, and I haven’t changed the plugin, theme, or gateway settings recently.

Environment details
• WordPress + WooCommerce
• Plesk-managed VPS, PHP 8.1, NGINX reverse proxy
• Cloudflare active (orange-cloud DNS, “Under Attack” mode occasionally enabled)

What I’m looking for
1. Identify the root cause of the “unable to complete payment” issue.
2. Apply a clean, secure fix so card payments succeed again.
3. Verify that PayPal and other gateways remain unaffected.
4. Provide a brief report outlining the fault, the steps you took, and any preventive recommendations (e.g., Cloudflare rule tweaks or additional Plesk settings).

Access provided
• WordPress admin and Plesk panel credentials
• Cloudflare dashboard (if DNS/firewall rules need adjustment)
• Staging site on request for testing outside production traffic

Success criteria
• A live test order processes end-to-end with credit/debit cards.
• No new checkout errors for 24 hrs after deployment.
• Core files remain untouched; solutions use hooks, settings, or overrides where possible.

If you’ve debugged WooCommerce on Plesk/Cloudflare stacks before and can jump on this quickly, I’m ready to grant access right away.