I am trying to render my sprites. I have created a shader in VOPs and passed it into SHOPs and used it in the sprite POP in my popnet. In theory it should work. I am rendering with mantra. There seems to be no or very little documentation on this area. Has anyone any idea where I could be going wrong?

Unfortunately, the sprites created through the sprite POP are for efficient visualization in the viewport. They are not directly supported by mantra at the current time. You'll have to use a combination of lookat (to orient particles to face the camera), and instancing textured grids.