Push Notification Integration (Flutter)

I need a Flutter developer to implement push notifications for an existing chat app on 'Android'. The notifications should alert users of new messages. Our app is completed, and now this is the only feature that's left, and we are looking for a flutter developer to implement it.

Requirements:
- Implement push notifications for new messages.
- Notifications should only work when the app is in the background, or haven't yet seen the message

Ideal Skills:
- Proficiency in Flutter and Android development
- Experience with Firebase Cloud Messaging (FCM) or similar services
- Knowledge of push notification integration