Breeding rays is not hard.. They are livebearers, and reproduce quite prolifically if given the right conditions..
Condition the adult pair with LOTS of high protein food, multiple times a day.. Which means your water quality might dip, so they need LOTS of fresh water too.. The bigger the pond and more water volume you work with, the better. When birthing happens, it releases a massive amount of body fluids into the water, another good reason to have good filtration and big water volume..
Lots of threads discussing breeding.. Read up here in the Ray section!