You will need to create a Gamer Server Login Token (GSLT) to use your CS:GO server. Here is how to create that token:
Step 1: Using your preferred browser, navigate to http://steamcommunity.com/dev/managegameservers
Step 2: You will need to login to your steam account. Once logged, you should see a screen like this, please enter 730 for the game id: 
Step 3: If you receive an error, you will need to add a phone number to your Steam account via this URL: https://store.steampowered.com/phone/add
Step 4: Take note of the token that is provided as you will need it in a few steps
Step 5: Once completed, log in to your Host Havoc game panel.
Step 6: Click on the command line manager.
Step 7: Create a custom command line and in the section+sv_setsteamaccount add the token you were provided.- Save your command line and select it.