Error: Load denied by X-Frame-Options
On WHMCS control panel, Virtualizor enduser panel fails to load with browser error:
Load denied by X-Frame-Options: https://YOUR_WHMCS_DOMAIN/admin/clientsservices.php?vapi_mode=1&userid=1&id=4&give=index.html#act=vpsmanage does not permit framing.
Verify X-Frame-Options value is not set to "deny" under your WHMCS web server configuration. If it is, then change it to "sameorigin" and restart the web service.
You will need to set id=domain or id=tab1 in your custom clientarea theme in clientareaproductdetails.tpl file.
If it still fails to load then you can disable cloudflare momentarily and see if that helps.
If the control panel is loading slower than expected when compared to loading of control panel on Virtualizor Enduser panel, then you can change the hostname field in Admin area on WHMCS order page to some other hostname (test1 in the image) or an FQDN which resolves to an IP (and does not takes time to resolve) and see if that helps :