sick toad
Hello,
It would be useful to have more details but one thing you might wish to check is cleanliness - toads and other amphibians can be deceiving because you rarely if ever see waste products. Never-the-less, ammonia and other toxins will build up over time, even if the substrate, such as soil or paper towels, appears "clean" to the eye. Same goes for the water bowl.
Also, toads purchased from pet stores are usually wild -caught and likely carry a variety of internal parasites. Parasites that cause few problems in the wild may kill a newly captured animal if its immune system is not working properly due to stress. Also, parasites can build up much larger populations in terrariums than in the wild, due to the enclosed space, especially if the substrate is not changed regularly.