So either a number is dividable by 3 "or" 5 or if it's not dividable by neither
3 or 5 it wants the program to return 0 as it seems because that's what my code does.
As an example, if you used the number 23 as input it would neither be dividable
by 3 or 5 so it would return 0 and apparently the test doesn't seem to care about
that or sees that as correct.

But it wants you to find the sum of all the multiples of 3 or 5 less than the input number. It doesn't matter if the input itself if a multiple of 3 or 5 or whatever.

23 should return the sum of all numbers below 23 that are multiples of 3 or 5

Out of curiosity, did you get an error message like: "(some number) should equal 23"?