You need to make two separate boxes that intersect at an edge, instead of one box with a line through the middle.

@mikelucas62, Supernoodle2014 is right. You must make the outlines as two separate shapes with the edge(s) to be V-cut edge straight and overlapping. You could for example have a single square board with a V-cut along the diagonal to create a two triangular boards (although the square would have to be rotated through 45 degrees to make the V-cut edge horizontal or vertical) but you cannot have curved, staggered or otherwise interrupted or irregular edges for V-cutting. So for example you could not have a circular board from which you V-cut a Yin and Yang pair. :) This may help: [https://easyeda\.com/forum/topic/TWO\_PCB\_ONE\_BOARD\-CqkCUO6oF](https://easyeda.com/forum/topic/TWO_PCB_ONE_BOARD-CqkCUO6oF)