Enter the network name, password and click "Create".

Step 2: Ask your friends to join the network
Send your friends the name of the Radmin VPN network and the password to join to this network.

Step 3: Run Project Zomboid

Step 4: Add the game to the firewall exceptions
You need to add rules to the firewall. Open "Radmin VPN -> System -> Firewall Exceptions" and add "ProjectZomboid64.exe" to the exceptions.

Step: 5 Host the game
Go to "Steam -> Library -> Project Zomboid". Right-click to select "Properties".

In the window that appears, go to the "Betas" section. Select "b41multiplayer" option.

Launch the game and in the main menu click "Host".

Click "Manage settings".

Click "Create New Settings".

Enter a name for new settings and click "Next".

There are a lot of game settings here, this time you don’t need to change anything and click "Save".

Click "Back".

Select the "Server name" and and select the required amount of "Server memory".

Click "Start".

Select Spawn Location and click "Next".

Select Occupation and Traits and click "Next".

Customize your character and click "Play".

Game client setup

Step 1: Install Radmin VPN and connect to the network
Download and install Radmin VPN. In the main Radmin VPN window, click "Join Network". Enter the Network Name and Password and click "Join". 

Make sure you and your friends are on the same network.

Step 2: Run Project Zomboid

Step 3: Add Rules to the Firewall
You need to add rules to the firewall. Open "Radmin VPN -> System -> Firewall Exceptions" and add "ProjectZomboid64.exe" to the exceptions.

Step 4: Join the game
Go to the main menu Project Zomboid and click "Join".

In the window that appears, enter the name of the server, IP and port of the game server (you can take the IP and port from Radmin VPN). If the server requires a password, enter it. Create your "Account Username" and "Account Password". Click "Add".

Then use the "Refresh" button.

After the server appears in the list, you can click "Join Server" button.

Now you can enjoy the game with your friends.