sort_custom() not sorting vector2i by y

[spark oxide]

I'm trying to sort all the vectors I have in an area by their y value, but it doesn't actually sort by anything, as shown in the output image.
I searched around and this seems the correct way to sort vectors by y, so I'm quite stuck as to why I'm getting this problem.

Sorry, I misread the way of using functions as custom sort, i was using a lambda function instead