The following article will cover the steps needed to make your DeadPoly Server Hosted By Host Havoc private.
1. Log into your game panel.
2. Stop your service if it is running.
3. Click on in your game panel and then click on either the or for the Engine.ini file.
4. Locate the Allowed Players List section and replace the numeric portion of the allow= section with your Steam64 ID and then click on
If using the portion, you will need to first enable the "Private" section to unhide the allowed list.
To add more than one allowed, you can copy and paste additional lines and then follow the above steps.
To locate your Steam64 ID, you can use a tool such as this https://www.steamidfinder.com/ or view your web console while logging in.