[2022] Friend can't join my Radmin VPN Server?

Hello, me and my friend have been trying to figure this out for a while now and we don't know what's making it not work. We're trying to play together privately through Radmin VPN. In Radmin, it shows that we're connected to the same network and it has worked for other games such as Roguelands. But when I make the server using the Unturned Dedicated Server app in Steam, only I can join it. When he puts in the IP and port, it just tries to join for a minute then fails. We don't know what we're doing wrong, so any help would be greatly appreciated. Thank you!