The game has some strict licencing requirements, so it would help if you could be quite a bit more specific about a few things.
  • Which editions of the game have you bought for PC? Which expansions?
  • Which editions of the game have you bought for Mac? Which expansions?
  • Have you registered all of the above to the same SquareEnix account via mogstation?
  • Did you register all of the above to the same FFXIV Service Account?
  • Are you signing into both clients with the same SquareEnix account?
  • Instead of going to character select, go to Data Center selection and chose your data center. Before taking you to character select, does a popup appear asking you to choose between two different Final Fantasy XIV Service Accounts?