You need to change the package name first before you get started. This is necessary step to make sure your application connects to Firebase Cloud Messaging service successfully in later step.
In Android Studio, you can do this by following below steps:
For example, if you want to change org.rbsoft.smsgateway to com.example.app, then:
In your Project pane, click on the little gear icon ( ).
Uncheck / De-select the Hide Empty Middle Packages option.
Your package directory will now be broken up in individual directories.
Individually select each directory you want to rename, and:
Right-click it.
Select Refactor.
Click on Rename.
In the Pop-up dialog, click on Rename Package instead of Rename Directory.
Enter the new name and hit Refactor.
Click Do Refactor in the bottom.
Allow a minute to let Android Studio update all changes.
Note: When renaming org in Android Studio, it might give a warning. In such case, select Rename All.
Now open your Gradle Build File (build.gradle - Usually app or mobile). Update the applicationId to your new Package Name and Sync Gradle, if it hasn't already been updated automatically.
You may need to change the package= attribute in your manifest.
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