I snet this a couple days ago and I never got any resolution to this. This plug in was the reason I signed up.
Here is my original support request.
I just installed the plug-in with no problem, however when I went to use it after I put in the remote host information, (https://starlitehosting.com/whmcs/) I get this php error:
Fatal error: Call to undefined function mb_strrchr() in /home/starligh/public_html/wp-content/plugins/whmcs-wordpresss-integration/lib/url_to_absolute.php on line 119