I have created an application using Flutter, and it runs correctly. The problem occurred when I tried to upload it to the Play Store. They asked me to update the

namespace com.example.hydraulic_employee 

and the

applicationId com.example.hydraulic_employee 

because I cannot use the word ‘example.’ I made the changes in the build.gradle and google-services.json files, but then I received this error:

Launching libmain.dart on sdk gphone64 x86 64 in debug mode...
Running Gradle task 'assembleDebug'...                             54.8s
√  Built buildappoutputsflutter-apkapp-debug.apk.
Installing buildappoutputsflutter-apkapp-debug.apk...           7.2s
E/AndroidRuntime(15400): FATAL EXCEPTION: main
E/AndroidRuntime(15400): Process: com.simbrainsolutions.hydraulic_employee, PID: 15400
E/AndroidRuntime(15400): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.simbrainsolutions.hydraulic_employee/com.simbrainsolutions.hydraulic_employee.MainActivity}: java.lang.ClassNotFoundException: Didn't find class "com.simbrainsolutions.hydraulic_employee.MainActivity" on path: DexPathList[[zip file "/data/app/~~sq5QywKCAXbNrdsSe4bbbw==/com.simbrainsolutions.hydraulic_employee-XUEIJt1wNJ6QQDBmEYwMxQ==/base.apk"],nativeLibraryDirectories=[/data/app/~~sq5QywKCAXbNrdsSe4bbbw==/com.simbrainsolutions.hydraulic_employee-XUEIJt1wNJ6QQDBmEYwMxQ==/lib/x86_64, /data/app/~~sq5QywKCAXbNrdsSe4bbbw==/com.simbrainsolutions.hydraulic_employee-XUEIJt1wNJ6QQDBmEYwMxQ==/base.apk!/lib/x86_64, /system/lib64, /system_ext/lib64]]
E/AndroidRuntime(15400):        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3551)
E/AndroidRuntime(15400):        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3782)
E/AndroidRuntime(15400):        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:101)
E/AndroidRuntime(15400):        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
E/AndroidRuntime(15400):        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
E/AndroidRuntime(15400):        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2307)
E/AndroidRuntime(15400):        at android.os.Handler.dispatchMessage(Handler.java:106)
E/AndroidRuntime(15400):        at android.os.Looper.loopOnce(Looper.java:201)
E/AndroidRuntime(15400):        at android.os.Looper.loop(Looper.java:288)
E/AndroidRuntime(15400):        at android.app.ActivityThread.main(ActivityThread.java:7872)
E/AndroidRuntime(15400):        at java.lang.reflect.Method.invoke(Native Method)
E/AndroidRuntime(15400):        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548)
E/AndroidRuntime(15400):        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:936)
E/AndroidRuntime(15400): Caused by: java.lang.ClassNotFoundException: Didn't find class "com.simbrainsolutions.hydraulic_employee.MainActivity" on path: DexPathList[[zip file "/data/app/~~sq5QywKCAXbNrdsSe4bbbw==/com.simbrainsolutions.hydraulic_employee-XUEIJt1wNJ6QQDBmEYwMxQ==/base.apk"],nativeLibraryDirectories=[/data/app/~~sq5QywKCAXbNrdsSe4bbbw==/com.simbrainsolutions.hydraulic_employee-XUEIJt1wNJ6QQDBmEYwMxQ==/lib/x86_64, /data/app/~~sq5QywKCAXbNrdsSe4bbbw==/com.simbrainsolutions.hydraulic_employee-XUEIJt1wNJ6QQDBmEYwMxQ==/base.apk!/lib/x86_64, /system/lib64, /system_ext/lib64]]      
E/AndroidRuntime(15400):        at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:259)
E/AndroidRuntime(15400):        at java.lang.ClassLoader.loadClass(ClassLoader.java:379)
E/AndroidRuntime(15400):        at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
E/AndroidRuntime(15400):        at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:95)
E/AndroidRuntime(15400):        at androidx.core.app.CoreComponentFactory.instantiateActivity(CoreComponentFactory.java:45)
E/AndroidRuntime(15400):        at android.app.Instrumentation.newActivity(Instrumentation.java:1339)
E/AndroidRuntime(15400):        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3538)
E/AndroidRuntime(15400):        ... 12 more

I updated the word example by simbrainsolutions.

this is the build.gradle file:

plugins {
    id "com.android.application"
    id "kotlin-android"
    id "dev.flutter.flutter-gradle-plugin"
    id 'com.google.gms.google-services'
}

def localProperties = new Properties()
def localPropertiesFile = rootProject.file('local.properties')
if (localPropertiesFile.exists()) {
    localPropertiesFile.withReader('UTF-8') { reader ->
        localProperties.load(reader)
    }
}

def flutterVersionCode = localProperties.getProperty('flutter.versionCode')
if (flutterVersionCode == null) {
    flutterVersionCode = '1'
}

def flutterVersionName = localProperties.getProperty('flutter.versionName')
if (flutterVersionName == null) {
    flutterVersionName = '1.0'
}

def keystoreProperties = new Properties()
def keystorePropertiesFile = rootProject.file('key.properties')
if (keystorePropertiesFile.exists()) {
    keystoreProperties.load(new FileInputStream(keystorePropertiesFile))
}

android {
    namespace "com.simbrainsolutions.hydraulic_employee"
    compileSdkVersion flutter.compileSdkVersion
    ndkVersion flutter.ndkVersion

    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }

    kotlinOptions {

        jvmTarget = '1.8'
    }

    sourceSets {
        main.java.srcDirs += 'src/main/kotlin'
    }

    defaultConfig {
        // TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).
        applicationId "com.simbrainsolutions.hydraulic_employee"
        // You can update the following values to match your application needs.
        // For more information, see: https://docs.flutter.dev/deployment/android#reviewing-the-gradle-build-configuration.
        minSdkVersion flutter.minSdkVersion
        targetSdkVersion flutter.targetSdkVersion
        versionCode flutterVersionCode.toInteger()
        versionName flutterVersionName
        multiDexEnabled true

    }

    // buildTypes {
    //     release {
    //         // TODO: Add your own signing config for the release build.
    //         // Signing with the debug keys for now, so `flutter run --release` works.
    //         signingConfig signingConfigs.debug
    //     }
    // }

    signingConfigs {
       release {
           keyAlias keystoreProperties['keyAlias']
           keyPassword keystoreProperties['keyPassword']
           storeFile keystoreProperties['storeFile'] ? file(keystoreProperties['storeFile']) : null
           storePassword keystoreProperties['storePassword']
       }
   }
   buildTypes {
       release {
           signingConfig signingConfigs.release
       }
   }

}

flutter {
    source '../..'
}

dependencies {
    implementation "androidx.multidex:multidex:2.0.1"

    implementation platform('com.google.firebase:firebase-bom:30.2.0')

    implementation 'com.google.firebase:firebase-analytics'

}

and this is the google-services.json:

{
  "project_info": {
    "project_number": "xxx",
    "project_id": "hydraulic-748ae",
    "storage_bucket": "hydraulic-748ae.appspot.com"
  },
  "client": [
    {
      "client_info": {
        "mobilesdk_app_id": "1:111178692999:android:3dc290cdf5ee57775c0e02",
        "android_client_info": {
          "package_name": "com.simbrainsolutions.hydraulic_employee"
        }
      },
      "oauth_client": [],
      "api_key": [
        {
          "current_key": "xxx"
        }
      ],
      "services": {
        "appinvite_service": {
          "other_platform_oauth_client": []
        }
      }
    }
  ],
  "configuration_version": "1"
}```

how can I fix the error ? 
*I am new to this kind of work 'hosting'*

I tried searching extensively on Google and Stack Overflow, but I couldn't find the answer.