Lumen help
Note: If your domain uses both A and AAAA records, you need to remove the AAAA record before attempting to provision the certificate. The Lumen platform uses IPv4, so AAAA records (which are IPv6) will be not pointing at Lumen platform leading to provision failure.
To create a free certificate using Let's Encrypt:
Once the certificate has been provisioned, it will automatically renew every 3 months.