I made a firestore database that looks like this.

I'm trying to make "stocks : 999" value change, so that it can be 998, 997, etc...

So I followed given instructions on firebase documentation (https://firebase.google.com/docs/firestore/manage-data/add-data#web-version-9_8), but I bump into an error when trying to make it work.

const [stock, SetStock] = useState([]);
const toUpdate = doc(db, "stocks", "stocks");

  useEffect(
    () =>
      onSnapshot(collection(db, "stocks"),(snapshot) => 
      SetStock(snapshot.docs[0].data().stocks)
     ),
 [] 
 );
 
 const update = () => {
   updateDoc(toUpdate, {
    stocks : increment(-1)
  });
  
 }

In here, the important things are const toUpdate = doc(db, "stocks", "stocks") and const update = ()..., the other are working great.

Anyways, after clicking the button that triggers "update", I get an error that says

Why ?

By the way, I am using React, I don't know if this might be useful.