is the full line you are looking at:
Domains (zones) consume credits on a monthly basis to remain active. These domains will automatically consume a credit each month with no action needed on your part. To stop the consumption of credits by a zone, simply delete that domain. If you have no credits left in your account to consume, a zone will display a warning to visitors coming to your website through our nameservers indicating that the domain has expired, and if credits are not purchased to renew the domain within 30 days, it will be deleted.
if so the paragraph refers to Domains (zones), which is DNS only, not registration or renewal of an actual domain name.
regards.