I have 4 train stations built and 3 of them are connected, it wont let me send trains to the newest station. It just says building is not built yet and then when I click on that it says I have maxed out the allowed buildings. Do I have to upgrade the main station 4/4 to be able to add routes to the station? Or do i have to hit a certain rank to unlock more? I'm a 70 right now. Please help!