If the monthly cost is too high, consider these open-source or free alternatives:
There is no such thing as a working, permanent, free WHMCS license key that is legal and safe. License Key Whmcs Free
Searching for "free" license keys often leads to "nulled" software—versions where the licensing check has been illegally removed. If the monthly cost is too high, consider
WHMCS offers a "Starter" tier designed specifically for new businesses. It includes all the core features but is limited by the number of active clients, making it very affordable. License Key Whmcs Free
If you already have a paid WHMCS license, you can obtain additional "Development Licenses" for testing environments for free. WHMCS - The Ultimate Integration Guide - Brixly