You can add this on your Android Manifest
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.WAKE_LOCK" />
<uses-permission android:name="com.google.android.c2dm.permission.RECEIVE" />
<receiver
android:name="com.google.firebase.iid.FirebaseInstanceIdReceiver"
android:exported="true"
android:permission="com.google.android.c2dm.permission.SEND" >
<intent-filter>
<action android:name="com.google.android.c2dm.intent.RECEIVE" />
<action android:name="com.google.android.c2dm.intent.REGISTRATION" />
<category android:name="YOUR PACKAGE NAME" />
</intent-filter>
</receiver>
<receiver
android:name="com.google.firebase.iid.FirebaseInstanceIdInternalReceiver"
android:exported="false" />
And then you can get the token and try to send Message on.
Dont forget also to build FirebaseApps on your code (in my case on my MainActivity)
FirebaseOptions options = new FirebaseOptions.Builder()
.setApiKey("YOUR FIREBASE API KEY")
.setApplicationId("YOUR FIREBASE APP ID")
.setGcmSenderId("YOUR FIREBASE SENDER ID")
.build();
FirebaseApp myApp = FirebaseApp.initializeApp(getApplicationContext(), options);
token = FirebaseInstanceId.getInstance(myApp).getToken();
Hope it will get what you looking for on Eclipse.