Kitty's won't use the litter box. Cats may not use a litter box for a variety of reasons. A cat has very sensitive paws and a sensitive nose. Consider the texture, quantity and scent of the litter that you buy. Moving the box to a quieter location.
Cats are very private creatures.
Daily cleaning might be needed. Do not use ammonia-based cleaning products as they have a smell similar to urine. Consulting a veterinarian. Inappropriate elimination may be a medical problem.