You can’t setup a server on dropbox. It’s not a server that you can connect to.
But you don’t even need that. If it’s a simple board game, then you can just use
the Listen Server. Watch the Multiplayer Tutorials from Epic on Youtube.
They tell you what a Listen Server is and how to use it.
There should be a board type game on the market. But i don’t know if it’s global
multiplayer or just turnbased local.