How to return data from Firestore query to a FlatList

Question

I'm new to React-Native and I am trying to return the array of data from the firstore query to the device screen where I can setDevices. I had this working using .get() and .then(), but I wasn't getting the updated events, so I've moved to onSnapshot and seem to have data at the query end, but can't get this set at the screen.

import React, { useEffect, useRef, useState } from "react";
import { Alert,FlatList,RefreshControl,StatusBar,Text,View } from "react-native";
import { TouchableOpacity } from "react-native-gesture-handler";
import styles from "./styles";
import { getDevices } from "../../services/devices";
import { useNavigation } from "@react-navigation/native";
import { Feather } from "@expo/vector-icons";
import CircularProgress from "react-native-circular-progress-indicator";
import { removeDevice } from "../../redux/actions";
import { useDispatch } from "react-redux";
import firebase from "firebase/app";
import "firebase/firestore";

const wait = (timeout) => {
  return new Promise((resolve) => setTimeout(resolve, timeout));
};

export default function DevicesScreen() {
  const [devices, setDevices] = useState([]);
  const [loading, setLoading] = useState(false);
  const componentMounted = useRef(true);
  const navigation = useNavigation();

  useEffect(() => {
    getDevices().then(setDevices)
  },[]);
  console.log()


TypeError: undefined is not an object (evaluating '(0, _devices.getDevices)().then')

This error is located at:
in DevicesScreen (created by SceneView)

This error appears. If I remove .then(setDevices) I can see the array of data on the console.log

import firebase from "firebase/app";
import "firebase/firestore";

export const getDevices = () => {
  firebase
    .firestore()
    .collection("device")
    .where("user_id", "==", "Rweeff9MO8XIDheZLx0HVbfaezy2")
    .get()
    .then((querySnapshot) => {
      querySnapshot.docs.map(doc => {
        let data =doc.data();
        console.log(data);
        return { id, ...doc };
      }
      )}
    )
  }

Thanks