This error is due to either a licensing issue,missing Curl and CurlSSL, IP address mismatch,misconfigured php.ini (/usr/local/lib/php.ini), strict rules in disable_functions option in php.ini, or PHP error.
Licensing Issue
The plugin requires that you open outgoing ports 443 (SSL) and 80 (HTTP). This is required for the script to check against our licensing server to check for the validity for the license and continue to execute. Should you receive aLicense status Invalid message, please be sure to create a file called "unixyvarnish.license" under "/etc/varnish/", if it exists. Or create the file "unixyvarnish.license" from within the installation directory. In both cases, the file must contain the license key that you were provided upon signup.
Example:
[root@varnish varnish.unixy.net]# pwd
/usr/src/varnish.unixy.net
[root@varnish varnish.unixy.net]# catunixyvarnish.license
Leased-cec3f81af739975b542ac688dasas30cc2
[root@varnish varnish.unixy.net]#
Missing Curl and/or CurlSSL
You'll need to install these two extension via cPanel/WHM EasyApache
IP Address Mismatch
Licensing of this plugin is per IP. Be sure you're accessing WHM using the IP that's listed in the product section in your Client Area.
PHP Error
If a PHP error occurs, you'll see an error log file called error_log in the current directory. Review the error and correct it. Then try again
disable_functions in /usr/local/lib/php.ini
Ensure curl_exec is not disabled in /usr/local/lib/php.ini. CURL is necessary for callbacks.
Make sure date.timezone is set correctly
Edit /usr/local/lib/php.ini and locate the date.timezone settings and put your timezone between single quotes like 'EST'