I am not an expert but here is what i learned from reading on here- First of all what are your temps and humidity? Flipping onto their back is a sign that they are stressed. Also frogs do not need UVB lighting and if it is too bright can stress them out. The soil he is on is good so no need for change there. The UTH should be on the side of the tank and not under since they burrow to cool off. Pacman frogs are not very active so they will stay in one spot for long periods of time. I think the best thing for him would be to limit contact with him and you can cover 3 sides of the tank with black construction paper to reduce stress. I would also change the UVB light to a regular light since they only need the light for a day - night cycle. Also moss is dangerous if you feed him inside the enclosure because if he tries to catch his prey on it he could miss and get some in his mouth and it can cause impaction.