Hi if it is the same as Ark, you set a password. Once there is a password anyone who want to join requires the password to access and play. You as the owner can change the password at any time and then redistribute it to the player's you want on your server.
Some people put the password and server in a forum allowing access to any who find it..
I didn't have any issues with my Ark server, however it was for select players only to stop looting by allow players.