A direct link to an HP-hosted driver file is available at ftp.hp.com (sp65184.exe). Quick Installation Guide

To use your HP A799 thermal printer with your computer, you need to install a driver. A printer driver is software that enables your computer to communicate with the printer and send print jobs. Without a driver, your printer will not be able to function properly.

Save that link. Avoid third-party driver sites. If the driver above doesn't work, run HP Print and Scan Doctor, or consider retiring the A799—it is nearly two decades old and not compatible with modern security or thermal paper workflows.