Blank PDF page problem will replicate on default WHMCS invoice and is related to missing required PHP extension. Make sure you have mbstring and iconv installed as PHP modules.

The file is corrupted error is related to outdated Ioncube Loader.  Please download and install latest Ioncube Loader version to resolve the problem. https://www.ioncube.com/loaders.php

Please check that PHP server configuration has allow_url_fopen = ON Our version checker also requires outgoing connection to Github API server.