Can't import MultiDexApplication

I have an app built with react native and I need to enable MultiDexsupport. My problem is that I can't import the MultiDexApplication class to extend it because at compile time I get symbol not found error for both the import statement and the class name when extending it in MainApplication.java

build.gradle

    dependencies {
        classpath('com.android.tools.build:gradle:3.5.3')
        classpath 'com.google.gms:google-services:4.2.0'
        classpath "androidx.multidex:multidex:2.0.1"

    }

If I try to add the dependency as implementation, I get the following error when starting the app:

Could not find method implementation() for arguments [androidx.multidex:multidex:2.0.1] on object of type org.gradle.api.internal.artifacts.dsl.dependencies.DefaultDependencyHandler.

In all online resources I saw that the dependecy was added as implementation so I guess that can be my problem.

MainApplication.java

package com.classmanager;

import android.app.Application;
import androidx.multidex.MultiDexApplication;
import android.content.Context;
import com.facebook.react.PackageList;
import com.facebook.react.ReactApplication;
import com.oblador.vectoricons.VectorIconsPackage;
import com.oblador.vectoricons.VectorIconsPackage;
import com.facebook.react.ReactNativeHost;
import com.facebook.react.ReactPackage;
import com.facebook.soloader.SoLoader;
import java.lang.reflect.InvocationTargetException;
import java.util.List;

public class MainApplication extends MultiDexApplication  implements ReactApplication {
  private final ReactNativeHost mReactNativeHost =
      new ReactNativeHost(this) {
        @Override
        public boolean getUseDeveloperSupport() {
          return BuildConfig.DEBUG;
        }

        @Override
        protected List<ReactPackage> getPackages() {
          @SuppressWarnings("UnnecessaryLocalVariable")
          List<ReactPackage> packages = new PackageList(this).getPackages();
          // Packages that cannot be autolinked yet can be added manually here, for example:
          // packages.add(new MyReactNativePackage());
          return packages;
        }

        @Override
        protected String getJSMainModuleName() {
          return "index";
        }
      };

  @Override
  public ReactNativeHost getReactNativeHost() {
    return mReactNativeHost;
  }

  @Override
  public void onCreate() {
    super.onCreate();
    SoLoader.init(this, /* native exopackage */ false);
    initializeFlipper(this); // Remove this line if you don't want Flipper enabled
  }

  //@Override
    //protected void attachBaseContext(Context base) {
       //super.attachBaseContext(base);
       //MultiDex.install(this);
    //}

  /**
   * Loads Flipper in React Native templates.
   *
   * @param context
   */
  private static void initializeFlipper(Context context) {
    if (BuildConfig.DEBUG) {
      try {
        /*
         We use reflection here to pick up the class that initializes Flipper,
        since Flipper library is not available in release mode
        */
        Class<?> aClass = Class.forName("com.facebook.flipper.ReactNativeFlipper");
        aClass.getMethod("initializeFlipper", Context.class).invoke(null, context);
      } catch (ClassNotFoundException e) {
        e.printStackTrace();
      } catch (NoSuchMethodException e) {
        e.printStackTrace();
      } catch (IllegalAccessException e) {
        e.printStackTrace();
      } catch (InvocationTargetException e) {
        e.printStackTrace();
      }
    }
  }
}

It's the default MainApplication from react-native init, except that I imported the MultiDexApplication class and extended it instead of Application. But when I run the app, I get the following error:

    import androidx.multidex.MultiDexApplication;
                        ^
  symbol:   class MultiDexApplication
  location: package androidx.multidex
C:\Users\meadi\WebstormProjects\ClassManager\android\app\src\main\java\com\classmanager\MainApplication.java:16: error: cannot find symbol
public class MainApplication extends MultiDexApplication  implements ReactApplication {
                                     ^
  symbol: class MultiDexApplication
C:\Users\meadi\WebstormProjects\ClassManager\android\app\src\main\java\com\classmanager\MainApplication.java:18: error: incompatible types: MainApplication cannot be converted to Application
      new ReactNativeHost(this) {
                          ^

Any idea why MultiDexApplication couldn't be resolved?

update: I tried adding the multidex dependecy as implementation to the app level build.gradle. It seems now that the class is resolved, but i get this error:

    D8: Cannot fit requested classes in a single dex file (# methods: 100718 > 65536)
com.android.builder.dexing.DexArchiveMergerException: Error while merging dex archives:
The number of method references in a .dex file cannot exceed 64K.

So MultiDex is still not enabled

from Can't import MultiDexApplication