What am I missing? (ATM problem)

I'm trying to solve the ATM problem. My code is passing the unit tests just fine but I keep getting the FAIL. Here's my function:

def checkio(data):
balance, withdrawal = data
for amount in withdrawal:
    if amount < balance and (amount % 5) == 0:
        balance -= amount
        balance -= 1
return balance

This passes the example tests, and many more.

I was partly confused about the instruction in the comments that:

#make sure you have enough money to withdraw,
#otherwise don't (return the same balance)

When you say "return the same balance" that implies if any of the withdrawal amounts is over the amount, the function is to return the original balance. But I got past that by reading the example tests. I wrote to those tests, and now it's still Failing. Any ideas why?