I cannot believe that showed up again. Apparently, it was a word introduced at some point but was removed long ago. What kind of exercise was it on and what had you written? It's so important to learn what triggers these errors. Was it on a Strengthen skills exercise etc? Thanks for the notification.
The dog's clothing." is one of the accepted translations and should have been accepted. However, if this was a listening exercise and they said "The dog's clothes." then that would be the only acceptable answer.
Otherwise, unless there was another issue "clothing" should have been accepted. If you have this problme again please send a screenshot or at least a copy paste of the exercise, your answer, and the comment you received so we can solve the problem.