The following story illustrates the hidden consequences of using a "free" or nulled WHMCS license. The Midnight Migration

Versions of WHMCS where the license verification code has been stripped out.

and found a site offering a "nulled" version that promised to bypass the $29.95/month fee. It looked identical to the real software, so he installed it and started signing up customers.

Using pirated software violates Terms of Service. Your hosting provider may suspend your entire server if they detect a fraudulent license.