Most likely, you do not have either the Central Station, the International Terminal, or the Busan Station built. It is also important to make sure they are connected together by train tracks. Without it, you will not be able to take part in the marathon. If all of the above conditions are met, but you are still unable to take part in the marathon, contact our team by pressing the button in the upper right corner of the screen, and they will do their best to help you!
Have fun playing the game!