Duplicate charges are resulting from customers resubmitting their order because they received an “Internal Server Error” message on our checkout page.
We created a staging site using a WordPress plugin so that technical personnel could run tests to determine the problem. The payment processor we are using is GoDaddy Payments. Their tech has spent a lot of time testing the site but cannot isolate the error.
The problem cannot be located and may be a conflict at the server level like security or caching features setup by our hosting provider.
Please let me know if you can identify this problem. Might php and js code be conflicted on the website? If so, how can that be fixed? Need help fast!
Kindly, see my suggestions for troubleshooting from below as follows:
You should see the challenged/blocked firewall events in the firewall events if you navigate to the Cloudflare dashboard → Security → Overview and lookup for Firewall events for the past 24hours or so. Once you find them, click on a particular one to find more details about it (user-agent, IP, HTTP version …). If yes, could you share some details which service was triggered that blocked you?
- you should see your origin host/server IP out there and user-agent like WP-cron or WordPress/version
Just in case, since it’s related to the WordPress, I’d suggest you to whitelist your origin host / server / hosting IP address by navigating to the Security → WAF → Tools → IP Access Rules with the action “allow” for your Website and try again.
It knows to happen due to the WordPress using HTTP/1.0 and empty user-agent, therefore while executing WP-Cron or some other related JSON/REST API request via plugin which triggers the WAF rules (as it should normally).
Could be if you’re using some kind of a plugin for gallery or lightbox effect, that the “Rocket Loader” feature is in conflict with the JavaScript and being enabled at Cloudflare dashboard → Speed → Optimization 
May I ask, have you tried disabling the Rocket Loader feature at the Cloudflare dashboard?
It might be some conflict with the scripts while loading them.
May I also ask if you’ve got Auto Minify options enabled for HTML, CSS & JS at Cloudflare dashboard? Try disabling them too.
Kindly, may I ask you to check out what option have you got selected by navigating to the Cloudflare dashboard → Caching → Configuration → find section “Browser Cache TTL” and make sure the selected option from the dropdown menu is “Respect Existing Headers”.
Furthermore, from the same menu, click on the blue button saying “Purge Everything” to flush the cache at Cloudflare Edge, just in case.
Wait for a minute or two.
Refresh a page in your Web browser, otherwise try clearing your Web browser cache or use a different Web browser to test out again.
Also, if you checked your Developer Console (F12), are there any error and/or warnings?
Otherwise, maybe the “Auto Minify” for HTML, CSS and/or JavaScript is checked at Cloudflare dashboard → Speed → Optimization, and makes some issues