I was solving the FizzBazz problem with python in checkio

def checkio (number: int)->str:
if number% 15 == 0:
return 'Fizz Buzz'
elif number% 5 == 0:
return "Buzz"
elif number% 3 == 0:
return 'Fiz'
else:
return number

Enter

Example:
Fizz Buzz
AssertionError: 6 is divisible by 3
, 25
And it will not be correct.
Could I ask the reason?