Application ID

ApplicationId is the main unique identifier of your application. The applicationId is not related to the package name, application Id can different or same with package name.

In an Android project, the applicationId refers to a unique identifier for your Android application package. This identifier is used to distinguish your app from others and is essential for various purposes, including app installation, updating, and compatibility checks. Generally using 3 word arrangements (can be more than 3 or less than 3), for example: com.app.cpux, or app.dreamspace.cpux

1. Open Gradle Scripts > build.gradle (Module: app)

2. Change the application ID with your own id name

3. Click Sync Now.

4. Change the id as unique as possible, because application id is very important used if you want to publish the application to the google play.

Important : your applicationId must be the same as the Android package name you created in the firebase console when you created google-services.json

Continue reading ... https://blog-dream-space.blogspot.com/2023/08/android-application-id.html