Android custom notification sound for FCM in Flutter not working

Question

I have a custom notification sound for FCM in my Flutter App working properly when I set the targetSdkVersion to 25 but once I change the targetSdkVersion to 28 default sound is played instead of custom sound.

I'm using plugin firebase_messaging 6.0.9

This is my AndroidManifest.xml

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="*********">

    <uses-permission android:name="android.permission.INTERNET"/>
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>


    <application

        android:name=".Application"
        android:label="*****"
        android:icon="@mipmap/ic_launcher">

        <meta-data android:name="com.google.android.geo.API_KEY"
                   android:value="*********"/>
        <meta-data
                android:name="com.google.firebase.messaging.default_notification_icon"
                android:resource="@mipmap/ic_notification" 
                />

        <activity
            android:name=".MainActivity"
            android:launchMode="singleTop"
            android:theme="@style/LaunchTheme"
            android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
            android:hardwareAccelerated="true"
            android:windowSoftInputMode="adjustResize">

            <meta-data
                android:name="io.flutter.app.android.SplashScreenUntilFirstFrame"
                android:value="true" />
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>
                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>
            <intent-filter>
                <action android:name="FLUTTER_NOTIFICATION_CLICK" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>

    </application>

</manifest>

And this is my payload:

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="*********">

    <uses-permission android:name="android.permission.INTERNET"/>
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>


    <application

        android:name=".Application"
        android:label="*****"
        android:icon="@mipmap/ic_launcher">

        <meta-data android:name="com.google.android.geo.API_KEY"
                   android:value="*********"/>
        <meta-data
                android:name="com.google.firebase.messaging.default_notification_icon"
                android:resource="@mipmap/ic_notification" 
                />

        <activity
            android:name=".MainActivity"
            android:launchMode="singleTop"
            android:theme="@style/LaunchTheme"
            android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
            android:hardwareAccelerated="true"
            android:windowSoftInputMode="adjustResize">

            <meta-data
                android:name="io.flutter.app.android.SplashScreenUntilFirstFrame"
                android:value="true" />
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>
                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>
            <intent-filter>
                <action android:name="FLUTTER_NOTIFICATION_CLICK" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>

    </application>

</manifest>