VM839:1 Uncaught (in promise) SyntaxError: Unexpected token < in JSON at position 0

Question

I have used fetch api and listed but in my code it shows Uncaught (in promise) SyntaxError: Unexpected token < in JSON at position 0 like this.In console i get data from api but i didn't get listed .This is my code ,

 function Category(){

    const [users, setUsers] = useState([]); 

    const fetchData = () => {
        fetch(CategoryDataService.getAll())
           .then(response => {
               console.log(response);
                return response.json()
            })
            .then(data => {
               setUsers(data)
        })
     }

    useEffect(() => {
      fetchData()
      }, [])

   return(
     <>
       < Sidebar />
          <h2 style={{textAlign:"center"}}>Category List</h2>
   
           <div>
              {users.length > 0 && (
              <ul>
                 {users.map(user => (
                  <li key={user.id}>{user.category_name}</li>
                ))}
             </ul>
              )}
          </div>
      < Footer/>
      </>
      );
    }
    export default Category;

please check this. I am just a beginner to react so fix this error and explain this error and why this came?