Calling native Kotlin code from Flutter. MethodHandler issue

Question

I want to be able to call a MethodChannel so I can retrieve and send data between Flutter and a 3rd party app but when I do so I get these errors from my Firebase Messaging and Flutter Local Notifications plugins.

[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: PlatformException(channel-error, Unable to establish connection on channel., null, null)

[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: MissingPluginException(No implementation found for method initialize on channel dexterous.com/flutter/local_notifications)

This is my MainActivity.kt

package com.package.name

import android.content.ContextWrapper
import android.content.Intent
import android.content.IntentFilter
import android.os.BatteryManager
import android.os.Build
import android.os.Bundle
import androidx.annotation.NonNull
import io.flutter.embedding.android.FlutterActivity
import io.flutter.embedding.engine.FlutterEngine
import io.flutter.plugin.common.MethodChannel
import io.flutter.plugins.firebase.messaging.FlutterFirebaseMessagingPlugin

class MainActivity: FlutterActivity() {
    private val CHANNEL = "samples.flutter.dev/battery"

   override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        flutterEngine?.plugins?.add(FlutterFirebaseMessagingPlugin())
    }
    override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
        MethodChannel(flutterEngine.dartExecutor.binaryMessenger, CHANNEL).setMethodCallHandler {
            // Note: this method is invoked on the main thread.
            call, result ->
            if (call.method == "getBatteryLevel") {
                val batteryLevel = getBatteryLevel()

                if (batteryLevel != -1) {
                    result.success(batteryLevel)
                } else {
                    result.error("UNAVAILABLE", "Battery level not available.", null)
                }
            } else {
                result.notImplemented()
            }
        }
    }
    private fun getBatteryLevel(): Int {
        val batteryLevel: Int
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            val batteryManager = getSystemService(BATTERY_SERVICE) as BatteryManager
            batteryLevel = batteryManager.getIntProperty(BatteryManager.BATTERY_PROPERTY_CAPACITY)
        } else {
            val intent = ContextWrapper(applicationContext).registerReceiver(null, IntentFilter(Intent.ACTION_BATTERY_CHANGED))
            batteryLevel = intent!!.getIntExtra(BatteryManager.EXTRA_LEVEL, -1) * 100 / intent.getIntExtra(BatteryManager.EXTRA_SCALE, -1)
        }
        return batteryLevel
    }
}

Flutter code invoking method channel

Future<void> getBatteryLevel() async {
  
  const platform = const MethodChannel('samples.flutter.dev/battery');
  try {
    final int result = await platform.invokeMethod('getBatteryLevel');
    print(result);
  } on PlatformException catch (e) {
    print('${e.message}');
  }
}