I am working on a module that has two windows(maps). SideA can see everything happening in one window, SideB the other.
When I launch the module it asks what side do you want to play. But after I go online and Sync up it forces each side to be the same side. I don’t seem to understand how you setup to choose sides and sync up online.
The problem sounds like you are trying to test it using 2 sessions with the same VASSAL password (Edit → Preferences → Personal). Sides are keys to Password.