Ok, I've added a test case to the description where the lack of bills of a kind is explained. Hope it helps.

The author hasn't logged in for more than 2 years, and I'm not a native english speaker either.
If you think explaining why that test should return false will help, I could add it to the description later. You're welcome.

If you have a better description propose it (just complaining won't help), as it is, it's very clear to me (and others), and not so much for you (and others). Bills aren't magic things that change their value or you can split them, I think that's pretty obvious.

The money can only be in bills, and bills cannot be split. The second 100 client cannot be satisfied because you cannot give her 75 change when you only have one 100 bill and 2 25 bills.

First client with a bill of 100, receives 3 bills of 25 (Vasya has only 2 bills of 25 left), so Vasya can't give the change to the other one. Not a kata issue. Nobody forces you to solve a kata, you can always skip it or forfeit.