unhandledRejection: ReferenceError: Cannot access 'firestore' before initialization

Question

I'm very new to next.js, and I'm developing an API with it, side that API I want to use firebase, so I set up firebase but when I try to call it, this error appears: "unhandledRejection: ReferenceError: Cannot access 'firestore' before initialization"

Code below.

Firebase config file

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

// For Firebase JS SDK v7.20.0 and later, measurementId is optional
const firebaseConfig = {
    apiKey: "*******",
    authDomain: "********",
    projectId: "*****",
    storageBucket: "*****",
    messagingSenderId: "****",
    appId: "****",
    measurementId: "****"
  };

//if(!firebase.apps.length){
   
//}
firebase.initializeApp(firebaseConfig);
const firestore = firebase.firestore();
export { firestore };

Firestore service

import { firestore } from './firebase';

export class Firestore {
    async getOne(collection, uid){
        const data = await firestore.collection(`${collection}/${uid}`).get();
        return await data.docs();
    }
}

API page

import {Firestore} from '../../utils/firestore';
const firestore = new Firestore();

const getBanners = () => {
    return firestore.getOne('settings','client');
    //return data;
}

export default function Handler(req,res){
    res.status(200).json({
        'name':"getBanners",
        'data': getBanners()
    });
}