no need for zero(initialValue)

You have to track the bills, not just dollar amounts. Your's would work if they only had $25 bills. Instead he specifies they either have $25 bills, $50 bills or $100 bills. No other denominations.

C# works as does Java

You probably read the question wrong as I initially did. There are only 25, 50 and 100 dollar bills (no increments or sub-types). It took 1 for-loop and several conditionals to solve it. No other data structures, recursion or functions needed.

If he made you track different payment amounts (given as nested arrays), evaluate whether or not the value was enough and then see if he could successfully get through the line (with multiple coin and dollar amounts), then it would definitely be a 5 kyu problem...

I passed 20 out of 21. Is there ANY way for me to see what the input is on the one that is still wrong?

This was way harder than the last ten 6kyu katas I did. I think this should be at least 5kyu or even 4kyu. It requires data structures, possible recursive loops, and several functions.

If it's easy that means it should be a higher kyu number.

Too easy. Should be 5 kyu or lower.

This is probably the cleanest, most logical solution.