How to play Heroes of Might and Magic III online via Hamachi?

Now that both players are members of the same network, you can create a server (new - network - TCP IP - server), and the second player does the same, but chooses "join".

The problem is that we can see and ping each other through Hamachi, and we're happy about it.
However, within the game itself, the "Join" button is inactive and grayed out.

We would greatly appreciate your help.