I will also advice you to continue paying monthly instead of buying the perpetual (owned) license.
With the monthly license, your script may be upgraded for free whenever there is a new update.
Updates are not just for security reasons as I have just read. The WHMCS team is adding exciting new features each 3 - 4 months and releases them into the updates. It will be a real loss of money if you do not profit of these features.
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