The Lexmark Cloud firmware update process uses the printer’s native proxy settings which are under; Settings > Network/Ports > HTTP/FTP settings in the printer’s web interface.
To resolve this issue, a manual one-time firmware update is needed to enable support for hostnames in the proxy address. After this is completed, future firmware updates can be done from Lexmark Cloud. Please refer to KB article Hostnames in HTTP/FTP proxy setting does not work, Hostnames in HTTP/FTP proxy setting does not work for more details.
Note: To know how to update the printer firmware, click here.