/**
 * @license
 * Copyright 2026 Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
import { NextFn, Observer, Unsubscribe } from '../interfaces/public-types';
import { MessagingService } from '../messaging-service';
/**
 * Subscribes to an event that the app instance is unregistered from FCM so the FID is no longer active.
 * Use this to notify your backend to remove this FID to prevent 404 errors on send.
 *
 * @param messaging - The {@link MessagingService} instance.
 * @param nextOrObserver - A function or observer object called with the unregistered FID.
 * @returns Unsubscribe function to stop listening.
 */
export declare function onUnregistered(messaging: MessagingService, nextOrObserver: NextFn<string> | Observer<string>): Unsubscribe;