Due to technical issues with CloudInit and CentOS 8 and lower, CloudInit is unable to correctly configure IPv4 if one or more IPv6 addresses are also associated with your VPS.
If you wish to utilize an older version of CentOS and require the removal of IPv6, this article (How can I downgrade my IPv6 by myself?) can assist in removing IPv6, allowing you to reinstall the VPS and obtain a functional IPv6 setup.
Alternatively, you can manually install CentOS and configure it yourself. However, for the most secure and convenient process, we recommend using a modern version of CentOS, which we also offer. Simply reinstall the VPS with a current version of CentOS (e.g., CentOS 9) for optimal performance and compatibility.