Fix Flutter In-App Notification Issue

I'm looking for an experienced Flutter developer to resolve a notification issue in my Android app. The notifications work properly when the user logs in, but they stop appearing after an hour of phone inactivity. We are using Firebase for notifications, and the current implementation involves custom code for in-app notifications.

Key Requirements:
- Diagnose and fix the issue causing notifications to stop after inactivity.
- Ensure notifications consistently appear, regardless of phone activity.
- Maintain the use of Firebase for notifications.
- Review and possibly optimize the existing custom code for background services.

Ideal Skills and Experience:
- Strong experience with Flutter and Android development.
- Familiarity with Firebase notifications and background services.
- Ability to troubleshoot and debug notification issues effectively.
- Experience with optimizing custom code for performance and reliability.

If you have the expertise to help resolve this issue, I would love to hear from you.

** i want solution to be deployed in two days.