using System.Collections.Generic;  
void Start () {
  // Uncomment this method to enable OneSignal Debugging log output 
  // OneSignal.SetLogLevel(OneSignal.LOG_LEVEL.INFO, OneSignal.LOG_LEVEL.INFO);
  
  // Replace 'YOUR_ONESIGNAL_APP_ID' with your OneSignal App ID.
  OneSignal.StartInit("YOUR_ONESIGNAL_APP_ID")
    .HandleNotificationOpened(HandleNotificationOpened)
    .Settings(new Dictionary<string, bool>() {
      { OneSignal.kOSSettingsAutoPrompt, false },
      { OneSignal.kOSSettingsInAppLaunchURL, false } })
    .EndInit();
  
  OneSignal.inFocusDisplayType = OneSignal.OSInFocusDisplayOption.Notification;
  
  // The promptForPushNotifications function code will show the iOS push notification prompt. We recommend removing the following code and instead using an In-App Message to prompt for notification permission.
  OneSignal.PromptForPushNotificationsWithUserResponse(OneSignal_promptForPushNotificationsResponse);
  
  private void OneSignal_promptForPushNotificationsResponse(bool accepted) {
    Debug.Log("OneSignal_promptForPushNotificationsResponse: " + accepted);
  }
}

// Gets called when the player opens the notification.
private static void HandleNotificationOpened(OSNotificationOpenedResult result) {
}

<?xml version="1.0" encoding="utf-8" standalone="no"?>
<manifest xmlns:amazon="http://schemas.amazon.com/apk/res/android" xmlns:android="http://schemas.android.com/apk/res/android" android:installLocation="auto" package="COM.YOUR.PACKAGE_NAME" platformBuildVersionCode="23" >
    <supports-screens android:anyDensity="true" android:largeScreens="true" android:normalScreens="true" android:smallScreens="true" android:xlargeScreens="true"/>
    <application android:debuggable="false" android:icon="@drawable/app_icon" android:isGame="true" android:label="@string/app_name" android:theme="@style/UnityThemeSelector">
        <activity android:configChanges="locale|fontScale|keyboard|keyboardHidden|mcc|mnc|navigation|orientation|screenLayout|screenSize|smallestScreenSize|touchscreen|uiMode" android:label="@string/app_name" android:launchMode="singleTask" android:name="com.unity3d.player.UnityPlayerActivity" android:screenOrientation="fullSensor">
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>
                <category android:name="android.intent.category.LAUNCHER"/>
                <category android:name="android.intent.category.LEANBACK_LAUNCHER"/>
            </intent-filter>
            <meta-data android:name="unityplayer.UnityActivity" android:value="true"/>
        </activity>
        
        <amazon:enable-feature android:name="com.amazon.device.messaging" android:required="false"/>
        <service android:name="com.onesignal.ADMMessageHandler" android:exported="false" />
        <receiver android:name="com.onesignal.ADMMessageHandler$Receiver"
                  android:permission="com.amazon.device.messaging.permission.SEND" >
          <intent-filter>
            <action android:name="com.amazon.device.messaging.intent.REGISTRATION" />
            <action android:name="com.amazon.device.messaging.intent.RECEIVE" />
            <category android:name="COM.YOUR.PACKAGE_NAME" />
          </intent-filter>
        </receiver>
    </application>
    <uses-feature android:glEsVersion="0x20000"/>
    <uses-feature android:name="android.hardware.touchscreen" android:required="false"/>
    <uses-feature android:name="android.hardware.touchscreen.multitouch" android:required="false"/>
    <uses-feature android:name="android.hardware.touchscreen.multitouch.distinct" android:required="false"/>
    
    <uses-permission android:name="com.amazon.device.messaging.permission.RECEIVE" />
    <permission android:name="COM.YOUR.PACKAGE_NAME.permission.RECEIVE_ADM_MESSAGE" android:protectionLevel="signature" />
    <uses-permission android:name="COM.YOUR.PACKAGE_NAME.permission.RECEIVE_ADM_MESSAGE" />
</manifest>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:amazon="http://schemas.amazon.com/apk/res/android"
    package="COM.YOUR.PACKAGE_NAME"
    android:versionCode="1"
    android:versionName="1.0" >

<uses-permission android:name="com.amazon.device.messaging.permission.RECEIVE" />
<permission android:name="COM.YOUR.PACKAGE_NAME.permission.RECEIVE_ADM_MESSAGE" android:protectionLevel="signature" />
<uses-permission android:name="COM.YOUR.PACKAGE_NAME.permission.RECEIVE_ADM_MESSAGE" />

<application>
  <amazon:enable-feature android:name="com.amazon.device.messaging" android:required="false"/>

  <service android:name="com.onesignal.ADMMessageHandler" android:exported="false" />
  <receiver android:name="com.onesignal.ADMMessageHandler$Receiver"
            android:permission="com.amazon.device.messaging.permission.SEND" >
    <intent-filter>
      <action android:name="com.amazon.device.messaging.intent.REGISTRATION" />
      <action android:name="com.amazon.device.messaging.intent.RECEIVE" />
      <category android:name="COM.YOUR.PACKAGE_NAME" />
    </intent-filter>
  </receiver>
</application>

#import "OneSignal.h"

#import "NotificationService.h"

@interface NotificationService ()

@property (nonatomic, strong) void (^contentHandler)(UNNotificationContent *contentToDeliver);
@property (nonatomic, strong) UNNotificationRequest *receivedRequest;
@property (nonatomic, strong) UNMutableNotificationContent *bestAttemptContent;

@end

@implementation NotificationService

- (void)didReceiveNotificationRequest:(UNNotificationRequest *)request withContentHandler:(void (^)(UNNotificationContent * _Nonnull))contentHandler {
    self.receivedRequest = request;
    self.contentHandler = contentHandler;
    self.bestAttemptContent = [request.content mutableCopy];
    
    [OneSignal didReceiveNotificationExtensionRequest:self.receivedRequest withMutableNotificationContent:self.bestAttemptContent];
  
    // DEBUGGING: Uncomment the 2 lines below and comment out the one above to ensure this extension is excuting
    //            Note, this extension only runs when mutable-content is set
    //            Setting an attachment or action buttons automatically adds this
    // NSLog(@"Running NotificationServiceExtension");
    // self.bestAttemptContent.body = [@"[Modified] " stringByAppendingString:self.bestAttemptContent.body];
    
    self.contentHandler(self.bestAttemptContent);
}

- (void)serviceExtensionTimeWillExpire {
    // Called just before the extension will be terminated by the system.
    // Use this as an opportunity to deliver your "best attempt" at modified content, otherwise the original push payload will be used.
    
    [OneSignal serviceExtensionTimeWillExpireRequest:self.receivedRequest withMutableNotificationContent:self.bestAttemptContent];
    
    self.contentHandler(self.bestAttemptContent);
}

@end