Hello and sorry to hear your frogs not well. If your frogs stomach is coming up you need to stop feeding till he goes to the bathroom, they usually do this when they are full to the tilt or if they have worms. So he is either full, and by the sounds of it this could be the problem or he has worms that you will need meds for from a vet. My guess is while trying to catch his food hes ingested a fair bit of moss and that's why when his stomach came out you were able to see moss. You need to go to a vet, and I will be honest even then I don't know if he will make it much longer. Most times a frog does this there isn't a very high survival rate. And if hes done it again it could be because he still hasn't got the excess food and moss out, or when his stomach went back in the first time it didn't go back into the right position. If It happens again from my understanding the best thing you can do is try to hold his mouth open till he pulls his stomach back in so he doesn't bite down on it causing more damage, or just leave him to do it himself. All and all I really think a vet visit would be the best thing.