After Change package name now you need to config the firebase (firebase its a google service used to send notification)
1. Go to Firebase Console, create new project - "Name the project whatever you want."
2. Click on Android to create Android App inside our project
3. Enter the Application Package Name, you will get in AndroidManifest.xml file and click on register.
4. Download the Json file and paste/replace in app folder
Please note
- Don't try to generate APK without config firebase
- Don't try To sync the project without config firebase