MethodChannal ccAvenuePayment not working

MainActivity.kt

class MainActivity: FlutterActivity() {

private val CHANNEL = "Method_Channel"
  lateinit  var inInit: OnHeadlineSelectedListener
  val result = MutableLiveData<String> ().apply { value = "" }
  interface OnHeadlineSelectedListener {
    fun onArticleSelected(position: Int)
  }
  override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
    val streamHandlerImpl = UpdateStackMemoryStream()
    inInit=streamHandlerImpl
    streamHandlerImpl.startListening(flutterEngine.dartExecutor)

    GeneratedPluginRegistrant.registerWith(flutterEngine)

    MethodChannel(flutterEngine.dartExecutor.binaryMessenger, CHANNEL).setMethodCallHandler {
      // Note: this method is invoked on the main thread.
      call, result ->
      if (call.method == "ccAvenuePayment") {
          Log.d("CALL","method : "+call.method) // NOT CALLED !!!
          val json = JSONObject(call.argument<String>("params"))
          val intent = Intent(this, mumbai.dev.testapp.MainActivity::class.java)
          intent.putExtra("currency",json.optString("currency"))
          intent.putExtra("amount",json.optDouble("amount"))
          intent.putExtra("custId",json.optString("custId"))
          intent.putExtra("param1",json.optString("param1"))
          startActivityForResult(intent,123)

      } else {
        result.notImplemented()
      }
    }

    val event = EventChannel(flutterEngine?.dartExecutor?.binaryMessenger,"trans")
    event.setStreamHandler(object : EventChannel.StreamHandler {
      override fun onListen(arguments: Any?, events: EventChannel.EventSink?) {
        this@MainActivity.result.observe(this@MainActivity, Observer {
          if (it?.isNotBlank() == true) {
            events?.success(it)
            Toast.makeText(this@MainActivity, "Call fluttwe", Toast.LENGTH_SHORT).show()
            result.postValue("")
          }
        })

      }

      override fun onCancel(arguments: Any?) {

      }

    })

  }
  override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
    if (resultCode == Activity.RESULT_OK && requestCode == 123) {
      val json = JSONObject(data?.getStringExtra("trans")?.trim())
      result.postValue(json.toString(1))
    }
  }


  // Checks if external storage is available for read and write
  fun isExternalStorageWritable(): Boolean {
    val state = Environment.getExternalStorageState()
    return if (Environment.MEDIA_MOUNTED == state) {
      true
    } else false
  }

  //Checks if external storage is available to at least read
  fun isExternalStorageReadable(): Boolean {
    val state = Environment.getExternalStorageState()
    return if (Environment.MEDIA_MOUNTED == state || Environment.MEDIA_MOUNTED_READ_ONLY == state) {
      true
    } else false
  }

  override fun onTrimMemory(level: Int) {
    if (level >= ComponentCallbacks2.TRIM_MEMORY_COMPLETE && android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.Q) {
      this.cacheDir.deleteRecursively()
      inInit.onArticleSelected(level)
    }
    super.onTrimMemory(level)
  }
}

wallet.dart

  void callCCAvenuePayment() async {
    print ("calling Android");
    try {
      var payment = PaymentParams(
          currency: globals.preferredCurrency,
          amount: double.parse(_viewModel.walletAmount.text.trim()),
          custId: globals.userid,
          param1: globals.phnNo ?? "");
      var accountToken=await platform.invokeMethod("ccAvenuePayment", {"params": jsonEncode(payment.toJson())});
      print("print result from CCAvenue: "+accountToken);

    } on PlatformException catch (e) {
      print("CCAvenue Call error"+e.message);
    }


  }

  EventChannel _stream = EventChannel('trans');
  
      _stream.receiveBroadcastStream().listen(
          (data) {
        setState(() {
          //_batteryLevel = batteryLevel;
       //   respController.text = data.toString();
          Toast().show(context: context, message: "Payed");
        });
      },
    );