Firebase Notification Always shows blank icon

This is the default behaviour of FCM. When app is in background it will take white icon.

Use this tag and put it in your Manifest. For me this worked. Hope it works for you too. Ensure meta-data is inside application like the example mentioned in quickstart

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme"
    tools:ignore="GoogleAppIndexingWarning">
    <!-- [START fcm_default_icon] -->
    <!-- Set custom default icon. This is used when no icon is set for incoming notification messages. -->
    <meta-data
        android:name="com.google.firebase.messaging.default_notification_icon"
        android:resource="@drawable/ic_stat_ic_notification" />
    <!-- Set color used with incoming notification messages. This is used when no color is set for the incoming
         notification message. -->
    <meta-data
        android:name="com.google.firebase.messaging.default_notification_color"
        android:resource="@color/colorAccent" />
    <!-- [END fcm_default_icon] -->
    <!-- [START fcm_default_channel] -->
    <meta-data
        android:name="com.google.firebase.messaging.default_notification_channel_id"
        android:value="@string/default_notification_channel_id" />
    <!-- [END fcm_default_channel] -->
    <activity
        android:name=".EntryChoiceActivity"
        android:label="@string/app_name">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

    <activity android:name=".kotlin.MainActivity" />
    <activity android:name=".java.MainActivity" />

If you are having this problem

See this link: Icon not displaying in notification: white square shown instead

I had the same problem. I solved by making transparent image from designer. Make sure your logo should be 72*72 pixels.

NOTE: Don't time waste in googling this issue, you just need a transparent icon which should be 72*72 dimensions.

The only thing that worked for me was to generate a Notification icon image asset in Android studio. To use the an image as the notification icon, just set Asset type to "Image" and select the file.

Tip #1: use an icon which is of white color, on transparent background!

Tip #2: if the preview on the right side of the window contains only white squares, your notification icon will look just like that - white squares!

Tip #3: the Name of the asset is what should be added into the meta-data tag in AndroidManifest

<meta-data
 android:name="com.google.firebase.messaging.default_notification_icon"
 android:resource="@drawable/whatever_you_set_for_image_asset_name" />

Source: Taken from this answer