If the specific HC configurations are correct, the issue may lie with the Steam client or network environment: Known Issues | Arma 3 | Official Website
A proven solution, particularly for x64 server builds, involves a simple, albeit unconventional, step. The error can sometimes occur because the necessary Steam services aren't fully initialized when the server executable starts. arma 3 headless client steam authentication failed hot
Ensure your HC launch command is correctly formatted. Common mistakes include missing quotes or incorrect ports. If the specific HC configurations are correct, the
The "Steam Authentication Failed" error is not a bug—it’s a rite of passage. Every experienced Arma admin has spent a late night cursing at a terminal, only to realize they forgot a single colon in their server.cfg . Once you conquer it, you join the ranks of those who truly understand the beautiful, janky, glorious machine that is Arma 3. Common mistakes include missing quotes or incorrect ports
Fixing Arma 3 Headless Client "Steam Authentication Failed" (Hot Fix Guide)
(found in %AppData%\Local\Arma 3 or server profile folder).