WHMCS has created its own module for automated game and voice server provisioning. Please see the following link for information on how this is setup.
If you are using the tcadmin_advanced module with WHMCS, please see this KB article for setup instructions.
*Please note that while automation can be great for your business, it also leaves you open to fraudulent orders if you do not check each order carefully.
If you are placing your system on automation so you do not have to watch it, you are opening yourself up to large problems with fraudulent transactions.