Hello and congrats on your new frog. Here is a nice article about their care: Frog Forum - Pacman and Horned Frogs - Ceratophrys - Care and Breeding. Recommend remove the moss because it is an impaction hazard. A better substrate is shredded coco (Plantation Soil or EcoEarth) mixed with dechlorinated water until slightly damp and clumps in fist without dripping water out.

Also, unless you are breeding and raising healthy parasite free guppies; feeding them to your frog is a risky food. Night Crawlers, Dubias and Crickets are better food items .