Free domains are an addition to your product offerings that can incentivize your customers to sign up for longer hosting plan terms.
Premium Domains are domains with short, common, memorable, or desirable names that sell for a higher price at your domain registrar.
In WHMCS, domain registrations are recurring products. WHMCS can automate management of these renewals through your domain registrar.
WHMCS can send domain renewal notices to your customers before their domain's due date and additional reminders after the due date passes.
After most domains expire, they enter a grace period and then a redemption grace period. Renewal during these periods may incur fees.