Payumoney integration with whmcs

Payumoney is providing itself gateway for whmcs. But that isn't wworking . I have Integrated it but after doing payment & Money is getting deducted. But payment isn't procceding in whmcs.

It it redirecting to a blank page /modules/gateways/call-back/response.php .

Whmcs is still showing invoice pending.

Whmcs version 8.1 latest.