I have a problem with my api. I want to use the firestore to input data for login & register with APi. Then, when i want to add the document database with user's input email when register but the output is error. my reasons for adding document with user's email is for easier for the next login step for its validation to compare the password also the email. here the code that i already make:

const functions = require("firebase-functions");
const express = require("express");
// eslint-disable-next-line no-unused-vars
const cors = require("cors");

const admin = require("firebase-admin");
admin.initializeApp();

const app = express();
const db = admin.firestore();

app.post("/Register", (req, res) => {
  const {
    name,
    email,
    password,
    phone,
  } = req.body;
  const saldo = 0;
  const valAcc = db.collection("Users").doc(email);
  valAcc.get().then((doc) => {
    if (doc.exists) {
      res.status(409).send("User Already Exist!");
    }
  });
  db.collection("Users").doc(email).add({
    Name: name,
    Email: email,
    Password: password,
    Phone: phone,
    Saldo: saldo,
  });
  res.status(201).send();
});

exports.apptest = functions.https.onRequest(app);

Do you guys have any solution? rly appriciate for any help.