Failed to resolve 'com.google.firebase:firebase-messaging:11.0.4' in Android Studio 2.3.3

Try to add Firebase features through firebase Assitance go to Tools then Firebase and then select which feature you want to add like Realtime Database. It will automatically add the compile dependencies to your project. I did the same and solved my problem.

Un Tick Offline Gradle Build will solve this issue if any of the above solution not working

As of 1-10-2020, this is what worked for me.

Top level build.gradle file:

buildscript {
    repositories {
        google()
        jcenter()
    }
    dependencies {
        classpath "com.android.tools.build:gradle:4.1.1"
        classpath 'com.google.gms:google-services:4.3.4'
    }
}    
allprojects {
    repositories {
        google()
        jcenter()
    }
}
task clean(type: Delete) {
    delete rootProject.buildDir
}

App level build.gradle file:

plugins {
    id 'com.android.application'
    id 'com.google.gms.google-services'
}
//Top code is same as= apply plugin: 'com.android.application'

android {
    compileSdkVersion 30
    buildToolsVersion "30.0.0"

    defaultConfig {
        applicationId "com.gc.pushnotificationssampleapp2"
        minSdkVersion 24
        targetSdkVersion 30
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}

dependencies {
    implementation 'androidx.appcompat:appcompat:1.2.0'
    implementation 'com.google.android.material:material:1.2.1'
    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
    testImplementation 'junit:junit:4.+'
    androidTestImplementation 'androidx.test.ext:junit:1.1.2'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'

    //Start of unique libs for this project:
    implementation 'com.google.firebase:firebase-messaging:20.0.1'
}

Make sure you have your app registered in Firebase. So you should have a google-services.json file in your project with your project's package name in it, something like this:

"client_info": {
  "mobilesdk_app_id": "1:551460864994:android:c0310a960a3afb06df2fbb",
  "android_client_info": {
    "package_name": "com.gc.pushnotificationssampleapp2"
  }

AndroidManifest.xml will need:

<uses-permission android:name="android.permission.INTERNET"></uses-permission>
. . . 
<service
    android:name=".FirebaseMessagingService">
    <intent-filter>
        <action android:name="com.google.firebase.MESSAGING_EVENT"/>
    </intent-filter>
</service>

Gradle version, firebase services version and google-play-services versions should be same when using. you may not use gradle 2.x with firebase core 16.x for example.

The solution is to update to the latest version of the classpath of com.google.gms:google-services

which is hinted by Android Studio in file build.gradle of the project

add in gradle

 Dependencies{
    
     // for the Firebase
        implementation platform('com.google.firebase:firebase-bom:26.5.0')
        implementation 'com.google.firebase:firebase-core:16.0.1'
        implementation 'com.google.firebase:firebase-messaging:20.1.3'
         implementation 'com.google.firebase:firebase-analytics:17.2.3'
    
    
    
    }
    
    apply plugin: 'com.google.gms.google-services'

and add in manifest

 <application>

     <service android:name=".util.FirebaseMessageReceiver"
            android:enabled="true"
            android:exported="true">
            <intent-filter>
                <action android:name="com.google.firebase.MESSAGING_EVENT" />
            </intent-filter>
        </service>


    </application>

and FirebaseMessageReceiver.java

this is with custom layout

    package com.---------.app.util;

import android.app.NotificationChannel;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.os.Build;
import android.widget.RemoteViews;

import androidx.core.app.NotificationCompat;

import com.google.firebase.messaging.FirebaseMessagingService;
import com.google.firebase.messaging.RemoteMessage;
import com.pisel.app.MainActivity;
import com.pisel.app.R;

public class FirebaseMessageReceiver
        extends FirebaseMessagingService {

    // Override onMessageReceived() method to extract the
    // title and
    // body from the message passed in FCM
    @Override
    public void
    onMessageReceived(RemoteMessage remoteMessage) {
        // First case when notifications are received via
        // data event
        // Here, 'title' and 'message' are the assumed names
        // of JSON
        // attributes. Since here we do not have any data
        // payload, This section is commented out. It is
        // here only for reference purposes.
        /*if(remoteMessage.getData().size()>0){
            showNotification(remoteMessage.getData().get("title"),
                          remoteMessage.getData().get("message"));
        }*/

        // Second case when notification payload is
        // received.
        if (remoteMessage.getNotification() != null) {
            // Since the notification is received directly from
            // FCM, the title and the body can be fetched
            // directly as below.
            showNotification(
                    remoteMessage.getNotification().getTitle(),
                    remoteMessage.getNotification().getBody());
        }
    }

    // Method to get the custom Design for the display of
    // notification.
    private RemoteViews getCustomDesign(String title,
                                        String message) {
        RemoteViews remoteViews = new RemoteViews(
                getApplicationContext().getPackageName(),
                R.layout.notification);
        remoteViews.setTextViewText(R.id.title, title);
        remoteViews.setTextViewText(R.id.message, message);
        remoteViews.setImageViewResource(R.id.icon,
                R.drawable.flag_belarus);
        return remoteViews;
    }

    // Method to display the notifications
    public void showNotification(String title,
                                 String message) {
        // Pass the intent to switch to the MainActivity
        Intent intent
                = new Intent(this, MainActivity.class);
        // Assign channel ID
        String channel_id = "notification_channel";
        // Here FLAG_ACTIVITY_CLEAR_TOP flag is set to clear
        // the activities present in the activity stack,
        // on the top of the Activity that is to be launched
        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        // Pass the intent to PendingIntent to start the
        // next Activity
        PendingIntent pendingIntent
                = PendingIntent.getActivity(
                this, 0, intent,
                PendingIntent.FLAG_ONE_SHOT);

        // Create a Builder object using NotificationCompat
        // class. This will allow control over all the flags
        NotificationCompat.Builder builder
                = new NotificationCompat
                .Builder(getApplicationContext(),
                channel_id)
                .setSmallIcon(R.drawable.flag_india)
                .setAutoCancel(true)
                .setVibrate(new long[]{1000, 1000, 1000,
                        1000, 1000})
                .setOnlyAlertOnce(true)
                .setContentIntent(pendingIntent);

        // A customized design for the notification can be
        // set only for Android versions 4.1 and above. Thus
        // condition for the same is checked here.
        if (Build.VERSION.SDK_INT
                >= Build.VERSION_CODES.JELLY_BEAN) {
            builder = builder.setContent(
                    getCustomDesign(title, message));
        } // If Android Version is lower than Jelly Beans,
        // customized layout cannot be used and thus the
        // layout is set as follows
        else {
            builder = builder.setContentTitle(title)
                    .setContentText(message)
                    .setSmallIcon(R.drawable.flag_british_indian_ocean_territory);
        }
        // Create an object of NotificationManager class to
        // notify the
        // user of events that happen in the background.
        NotificationManager notificationManager
                = (NotificationManager) getSystemService(
                Context.NOTIFICATION_SERVICE);
        // Check if the Android Version is greater than Oreo
        if (Build.VERSION.SDK_INT
                >= Build.VERSION_CODES.O) {
            NotificationChannel notificationChannel
                    = new NotificationChannel(
                    channel_id, "web_app",
                    NotificationManager.IMPORTANCE_HIGH);
            notificationManager.createNotificationChannel(
                    notificationChannel);
        }

        notificationManager.notify(0, builder.build());
    }
}

create a layout for notification design

  <!-- Parent Layout of ImageView -->
    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">

        <!--Image to be displayed beside the notification text-->
        <ImageView
            android:id="@+id/icon"
            android:layout_width="50dp"
            android:layout_height="50dp"
            android:padding="5dp"
            android:src="@drawable/flag_benin" />
    </LinearLayout>

    <!-- Parent layout for holding the Title and the Body-->
    <LinearLayout
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:orientation="vertical"
        android:padding="5dp">

        <!-- TextView for Title -->
        <TextView
            android:id="@+id/title"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Title"
            android:textColor="#000"
            android:textStyle="bold" />

        <!-- TextView for Body -->
        <TextView
            android:id="@+id/message"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Message"
            android:textSize="15sp" />

    </LinearLayout>

</LinearLayout>

For those who use firebase bom

implementation platform('com.google.firebase:firebase-bom:29.0.1')
// Firebase Cloud Messaging (Java)
    implementation 'com.google.firebase:firebase-messaging'

    // Firebase Cloud Messaging (Kotlin)
    implementation 'com.google.firebase:firebase-messaging-ktx'

    // For an optimal experience using FCM, add the Firebase SDK
    // for Google Analytics. This is recommended, but not required.
    implementation 'com.google.firebase:firebase-analytics'

I had the same problem. Later discovered I copied the line exactly from firebase docs.

Classpath 'com.google.gms:google-services:3.1.1'

Notice the CAPITAL 'C'.

it should be

classpath 'com.google.gms:google-services:3.1.1'

with lower case 'c'.

Dumb mistake but easily unnoticeable.