Is that a melon or a squash or cuke?

Hard to tell the size, but based on the stitching on the seam, it looks like it could be pretty small.

What is the problem? Hard to tell from the photo.

Looks like a silverline melon. I think incomplete pollination. It'll probably rot off, but you should get more.

Thanks for the feedback it is a melon.
The plant is still having problems, now one of the fruits has changed color from green to yellow
See attached picture

Good looking melon, Hope mine come out that good.