?Error in Substring function in react

function Banner() {    const [movie,setMovie] = useState([])    useEffect( () =>{        async function fetchData(){            const req = await axios.get("some API request")//req is a string for sure            setMovie(req)        }         fetchData();    },[])const desciption = movie.substring(0,15)return(<h1>    {desciption}    </h1>)