FirebaseError: Firebase: Error (auth/invalid-api-key).

안녕하세요!

강의대로 따라하다가 FirebaseError: Firebase: Error (auth/invalid-api-key). 오류가 나왔습니다.

model/firebase_client.ts 부분입니다.

import { initializeApp, getApps } from 'firebase/app';
import { Auth, getAuth } from 'firebase/auth';
import getConfig from 'next/config';

const { publicRuntimeConfig } = getConfig();

const FirebaseCredentials = {
  apiKey: publicRuntimeConfig.apiKey,
  authDomain: publicRuntimeConfig.authDomain,
  projectId: publicRuntimeConfig.projectId,
};

export default class FirebaseAuthClient {
  public static instance: FirebaseAuthClient;

  private auth: Auth;

  public constructor() {
    const apps = getApps();
    if (apps.length === 0) {
      console.log('firebase initializeApp');
      initializeApp(FirebaseCredentials);
    }
    this.auth = getAuth();
    console.log('firebase auth client constructor');
  }

  public static getInstance(): FirebaseAuthClient {
    if (!FirebaseAuthClient.instance) {
      FirebaseAuthClient.instance = new FirebaseAuthClient();
    }
    return FirebaseAuthClient.instance;
  }

  public get Auth(): Auth {
    return this.auth;
  }
}

next.config도 확인했습니다ㅠㅠ

.env 파일명도 확인했고, firebase일반설정에 들어가 웹 API 키도 확인하였습니다. 혹시몰라 깃허브 예제코드와도 비교했지만 해결하지 못했습니다ㅠㅠ 무슨 문제일까요?