First, you will need to login to your client area and download your copy of “WHMCS Clear Tickets Flags”.
From the client’s area left menu click “Services” -> “My Services”. Open the “View Details” box by click the arrow on the right, and click “Downloads”, in the following screen click the “Download” link.
Unzip the file, upload it to your WHMCS hooks folder (“includes/hooks”).
That’s all !