I don't know if this pop-up was in the game for some time or if it was added recently, but I for one noticed it just now and I have to say it's an amazing idea. Why?
1. Because it's a triggered event.
2. Because you have to dismiss it.
3. Because it's in your face, literally.
Rail Nation should expand on this idea and introduce these sort of pop-ups for other stuff, not only payment related (which I really don't mind). This is an excellent way of forcing new players understand the basics of the game and the general consensus of playing it (hauling, majorities, associations, city competition, end game, etc).
These events are way better than the tutorial, which needs a bit of rework (as others have stated already).