The list is always valid indeed; I think the problem you're having MIGHT be to do with the method you're using - if you used (like me) a left and right variable and increased/decreased them if it was bigger or smaller (aka two pointers) like i did then the problem is that you need to sort the list - not every list is sorted. This answer is very speicific but it applys for everything that needs to be sorted

The problem is your code doesn't always return a list. Add return [0, 0] at the end. The tests expect a list.

The input is fine, your code has a bug.