Firebase Next.js ビルド時のエラー (auth/invalid-api-key)

Error [FirebaseError]: Firebase: Error (auth/invalid-api-key).
・・・以下略

import firebase from './firebase';

export const environment = {
  production: true,
  hmr: false,
  firebase: {
    apiKey: "xxx-xxx",
    authDomain: "xxx.firebaseapp.com",
    databaseURL: "https://xxx.firebaseio.com",
    projectId: "xxx",
    storageBucket: "xxx.appspot.com",
    messagingSenderId: "xxx"
  }
};