In firestore documentation it says that merge: true is needed if we want to merge data, it doesn't work

Here is my code, which is very similar to the example, it always replaces the old stored value ​​with the new one

async function updateTotal() {
  const update = await db.collection("resources").doc(id).update({ "total": "500"}, { merge: true })
}

I really need it if you have a solution please