I recently purchased Ultimate General Gettysburg (I already own Ultimate General Civl War) for my Mac, and I want to play online against my brother-in-law, who has a PC. We get all the way to the point of accepting each others' invitations to play, but then are unable to connect. Any suggestions on how to overcome this? I currently have Mac OS X Yosemite and am planning to update to High Sierra. Also, are there any other strategic war games that are known to support cross-player multiplatform?