Object-Oriented Python: isinstance Challenge

I have no idea why this approach isn't working. I ran the code in a workspace and it worked just fine with the demo "appledog13.2" list. When I try to run it in the challenge, I get a Bummer that says the += operator can't be used for 'int' and 'list'. Where am I going wrong? I've included the challenge parameters and my code.

'Create a function named combiner that takes a single argument, which will be a list made up of strings and numbers. Return a single string that is a combination of all of the strings in the list and then the sum of all of the numbers. For example, with the input ["apple", 5.2, "dog", 8], combiner would return "appledog13.2". Be sure to use isinstance to solve this as I might try to trick you.'

def combiner(*args):
    nums = 0
    words = ''
    for item in args:
        if isinstance(item, str):
            words += item
        else:
            nums += item
    return words + str(nums)

I've edited my code after looking into other peoples' solutions. I'm assuming Kenneth's trick was including a list inside the list...?

def combiner(*args):
    nums = 0
    words = ''
    for item in args:
        if isinstance(item, (int, float)):
            nums += item
        elif isinstance(item, str):
            words += item
    return words + str(nums)

Now I'm getting a message that says only "Did not get the expected output".