1. when you go to the buy troops screen, select a creature, and press M (English, the maximum button) on the keyboard, you will see the number of creatures that can be purchased for the available money, or you will understand that the opponent has more money than the total cost of the creatures.
2. clicking the right mouse button on the small icon of your city to the right of the creature slots will show you the city. If you have 2 cities and the opponent has 1, clicking on the 2nd city will cause the game to crash.
conclusion: it should only apply to your own cities, not the cities of the current player.