Valve Anti-Cheat System brings out much more entertainment factors in the game. However, you can only enjoy it if you get past the “VAC was Unable to Verify your Game session” error. Vac was unable to verify your game session error appears when you try to matchmake, but something doesn’t go right. Whenever you go to a VAC secured server, VAC tries to verify your identity and your device for any possible cheat signatures. In many cases, users with cheat codes installed on PC receive the error “VAC was unable to verify.” Other times, VAC interrupts a user’s game in the middle if it detects any third-party modifications and advantages in the game. It is as simple as that. To resolve, please check out the following methods: Steam Client Refresh and Restart, Fix it by verifying officially, Apply Administrator Run for Steam Client, Deactivate the Antivirus programs on your PC, Deactivate VPN or Virtual Private Network Service on your PC. For more information visit: https://graphictutorials.net/vac-was-unable-to-verify-your-game-session/