Can't terminate site from WHMCS

I am able to setup WHMCS MU Provisioning plugin successful.
But where I am getting an error is when I want to terminate an account
This is the error am getting below
<b>Fatal error</b>: Call to undefined function wpmu_delete_blog() in <b>/home/adeff/public_html/wp-content/plugins/whmcs-multisite-provisioning/whmcs-mrp.php</b> on line <b>652</b><br />