Firestore won't let me one more map to they array

rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {
    match /items/{itemId} {
      allow read;
      allow create, update: if request.auth != null
      && request.resource.data.reviews.size() == 1
      && 'reviews' in request.resource.data
      && request.resource.data.reviews[0].keys().hasAll(['userId', 'rating', 'review', 'userName'])
      && request.resource.data.reviews[0].size() == 4
      && request.resource.data.reviews[0].userId == request.auth.uid
      && !(exists(/databases/$(database)/documents/items/$(itemId)/reviews/$(request.resource.data.reviews[0].userId)))
    }
  }
}

const handleSubmit = async () => {
    const itemRef = doc(db, "items", itemId);
    await updateDoc(itemRef, {
      reviews: arrayUnion({
        userId,
        rating,
        review,
        userName,
      }),
    });
  };